Apparatus and method of inserting spinal implants

ABSTRACT

Apparatus and a method of inserting spinal implants is disclosed in which an intervertebral space is first distracted, a hollow sleeve having teeth at one end is then driven into the vertebrae adjacent that disc space. A drill is then passed through the hollow sleeve removing disc and bone in preparation for receiving the spinal implant which is then inserted through the sleeve. Apparatus and a method of inserting spinal implants is disclosed in which an intervertebral space is first distracted to restore the normal angular relationship of the vertebrae adjacent to that disc space. An extended outer sleeve having extended portions capable of maintaining the vertebrae distracted in their normal angular relationship is then driven into the vertebrae adjacent that disc space. A drill is then passed through the hollow sleeve removing disc and bone in preparation for receiving the spinal implant which is then inserted through the sleeve.

RELATED APPLICATIONS

This is a continuation of application Ser. No. 08/396,414, filed Feb.27, 1995 now U.S. Pat. No. 6,080,155, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to artificial fusion implants to be placedinto the intervertebral space left remaining after the removal of adamaged spinal disc and specifically to the apparatus for and method of,inserting the implants.

2. Description of the Prior Art

For the purpose of achieving long term stability to a segment of injuredspine, a fusion (the joining together of two or more bones via acontinuous bridge of incorporated bone) may be performed. Well-known tothose skilled in such art is the interbody fusion wherein the disc ispartially excised and bone placed within that space previously occupiedby that disc material (between adjacent vertebrae) for the purpose ofrestoring a more normal spatial relationship, and to provide forstability; short term by mechanical support, and long term by thepermanent cross bonding of bone from vertebra to vertebra. For fusion tooccur within the disc space, it is necessary to prepare the vertebrae tobe fused by breaking through, or cutting into, the hardened outsideplates of bone (the endplates) to allow the interposed bone graft tocome into direct contact with the more vascular cancellous (spongy)bone, and to thereby trick the body into attempting to heal thisinduced, but controlled, “fracturing” by both bone production and thehealing of the grafts to both opposed vertebral surfaces such that theybecome one continuous segment of bone.

The purpose of the present invention is to provide an implant, and theapparatus and method of inserting the implant within the intervertebralspace left after the removal of the disc material and permanentlyeliminate all motion at that location. To do so, the device of thepresent invention is space occupying within the disc interspace, rigid,self-stabilizing to resist dislodgement, stabilizing to the adjacentspinal vertebrae to eliminate local motion, and able to intrinsicallyparticipate in a vertebra to vertebra bony fusion so as to assure thepermanency of the result.

At present, following the removal of a damaged disc, either bone ornothing is placed into the remaining space. Placing nothing into thisspace allows the space to collapse which may result in damage to thenerves; or the space may fill with scar tissue and eventually lead to areherniation. The use of bone to fill the space is less than optimal inthat bone obtained from the patient requires additional surgery and isof limited availability in its most useful form, and if obtainedelsewhere, lacks living bone cells, carries a significant risk ofinfection, and is also limited in supply as it is usually obtained fromaccident victims. Furthermore, regardless of the source of the bone, itis only marginal structurally and lacks a means to either stabilizeitself against dislodgement, or to stabilize the adjacent vertebrae.

a. Prior Art Implants

There have been an extensive number of attempts to develop an acceptabledisc prosthesis (an artificial disc). Such devices by design would beused to replace a damaged disc and seek to restore the height of theinterspace and to restore the normal motion of that spinal joint. Nosuch device has been found that is medically acceptable. This group ofprosthetic or artificial disc replacements, seeking to preserve spinalmotion and so are different from the present invention, would include:

U.S. Pat. No. 3,867,728 to STUBSTAD—describing a flexible disc implant.

U.S. Pat. No. 4,349,921 to KUNTZ—describing a flexible disc replacementwith file-like surface projections to discourage device dislocation.

U.S. Pat. No. 4,309,777 to PATIL—describing a motion preserving implantwith spiked outer surfaces to resist dislocation and containing a seriesof springs to urge the vertebrae away from each other.

U.S. Pat. No. 3,875,595 to FRONING—describing a motion preservingbladder-like disc replacement with two opposed stud-like projections toresist dislocation.

U.S. Pat. No. 2,372,622 to FASSIO (France)—describing a motionpreserving implant comprising complimentary opposed convex and concavesurfaces.

In summary, these devices resemble the present invention only in thatthey are placed within the intervertebral space following the removal ofa damaged disc. In that they seek to preserve spinal motion, they arediametrically different from the present invention which seeks topermanently eliminate all motion at that spinal segment.

A second related area of prior art includes those devices utilized toreplace essentially wholly removed vertebrae. Such removal is generallynecessitated by extensive vertebral fractures, or tumors, and is notassociated with the treatment of disc disease. While the presentinvention is to be placed within the disc space, these other vertebraldevices cannot be placed within the disc space as at least one vertebrahas already been removed such that there no longer remains a “discspace”. Furthermore, these devices are limited in that they seek toperform as temporary structural members mechanically replacing theremoved vertebrae (not a removed disc), and do not intrinsicallyparticipate in supplying osteogenic material to achieve cross vertebraebony fusion. Therefore, unlike the present invention which provides fora source of osteogenesis, use of this group of devices must beaccompanied by a further surgery consisting of a bone fusion procedureutilizing conventional technique. This group consisting of vertebralstruts rather than disc replacements would include the following:

U.S. Pat. No. 4,553,273 to WU—describing a turnbuckle-like vertebralstrut.

U.S. Pat. No. 4,401,112 to REZAIAN—describing a turnbuckle-likevertebral strut with the addition of a long stabilizing staple thatspans the missing vertebral body.

U.S. Pat. No. 4,554,914 to KAPP—describing a large distractible spikethat elongates with a screw mechanism to span the gap left by theremoval of an entire vertebra and to serve as an anchor for acryliccement which is then used to replace the missing bone (vertebrae).

U.S. Pat. No. 4,636,217 to OGILVIE—describing a vertebral strutmechanism that can be implanted after at least one vertebrae has beenremoved and consists of a mechanism for causing the engagement of screwsinto the vertebrae above and the vertebrae below the one removed.

In summary, this second group of devices differs from the presentinvention in that they are vertebral replacements struts, do notintrinsically participate in the bony fusion, can only be inserted inthe limited circumstances where an entire vertebra has been removed fromthe anterior approach, and are not designed for, or intended to be usedfor the treatment of disc disease.

A third area of prior art related to the present invention includes alldevices designed to be applied to one of the surfaces of the spine. Suchdevices include all types of plates, struts, and rods which are attachedby hooks, wires and screws. These devices differ significantly from thepresent invention in that they are not inserted within the disc spaceand furthermore do not intrinsically participate in supplying osteogenicmaterial for the fusion.

Therefore, where permanent spinal immobilization is desired, anadditional surgery, consisting of a spinal fusion performed byconventional means or the use of supplemental methylmethacrylate cementis required. Such devices applied to the spine, but not within the discspace, would include the following:

U.S. Pat. No. 4,604,995 to STEPHENS—describing a “U” shaped metal rodattached to the posterior elements of the spine with wires to stabilizethe spine over a large number of segments.

U.S. Pat. No. 2,677,369 to KNOWLES—describing a metal column device tobe placed posteriorly along the lumbar spine to be held in position byits shape alone and to block pressure across the posterior portions ofthe spinal column by locking the spine in full flexion thereby shiftingthe maximum weight back onto the patient's own disc.

Other devices are simply variations on the use of rods (e.g. Harrington,Luque, Cotrel-Dubosset, Zielke), wires or cables (Dwyer), plates andscrews (Steffee), or struts (Dunn, Knowles)

In summary, none of these devices are designed to be nor can be usedwithin the disc space. Moreover, these devices do not replace a damageddisc, and do not intrinsically participate in the generation of a bonyfusion.

Another area of related prior art to be considered is that of devicesdesigned to be placed within the vertebral interspace following theremoval of a damaged disc, and seeking to eliminate further motion atthat location.

Such a device is contained in U.S. Pat. No. 4,501,269 issued to BAGBYwhich describes an implantable device and limited instrumentation. Themethod employed is as follows: a hole is bored transversely across thejoint and a hollow metal basket of larger diameter than the hole is thenpounded into the hole and then the hollow metal basket is filled withthe bone debris generated by the drilling.

While the present invention (device, instrumentation, and method) mayappear to bear some superficial resemblance to the BAGBY invention, itis minimal, while the differences are many fold and highly significant.These differences include the following:

1. Safety—The present invention provides for a system of completelyguarded instrumentation so that all contiguous vital structures (e.g.large blood vessels, neural structures) are absolutely protected. Theinstrumentation of the present invention also makes overpenetration bythe drill impossible. Such overpenetration in the cervical spine, forexample, would result in the total paralysis or death of the patient. Inthe thoracic spine, the result would be complete paraplegia. In thelumbar spine, the result would be paraplegia or a life-threateningperforation of the aorta, vena cava, or iliac vessels.

The present invention is atraumatically screwed into place while theBAGBY device, in contradistinction, is pounded into position. BAGBYdescribes that its implant is significantly larger in size than the holedrilled and must be pounded in. This is extremely dangerous and thepounding occurs directly over the spinal cord which is precariouslyvulnerable to percussive injury. Furthermore, while it is possible, forexample in the lumbar spine, to insert the present invention away fromthe spinal cord and nerves, the BAGBY device must always be poundeddirectly towards the spinal cord.

Furthermore, since the BAGBY device is pounded into a smooth hole undergreat resistance, and lacking any specific design features to secure it,the device is highly susceptible to forceful ejection which would resultin great danger to the patient and clinical failure. The presentinvention, in contradistinction, is securely screwed into place, andpossesses highly specialized locking threads to make accidentaldislodgement impossible. Because of the proximity of the spinal cord,spinal nerves, and blood vessels, any implant dislodgement as mightoccur with the BAGBY device might have catastrophic consequences.

2. Broad applicability—The BAGBY device can only be inserted from thefront of the vertebral column, however, in contrast, the presentinvention can be utilized in the cervical, thoracic, and lumbar spine,and can be inserted from behind (posteriorly) in the lumbar spine. Thisis of great importance in that the purpose of these devices is in thetreatment of disc disease and probably greater than 99 percent of alllumbar operations for the treatment of disc disease are performed frombehind where the present invention can easily be utilized, but the BAGBYdevice, as per BAGBY'S description, cannot.

3. Disc removal—The BAGBY invention requires the complete removal of thedisc prior to the drilling step, whereas the present inventioneliminates the laborious separate process of disc removal andefficiently removes the disc and prepares the vertebral end plates in asingle step.

4. Time required—The present invention saves time over the BAGBYinvention since time is not wasted laboring to remove the disc prior toinitiating the fusion. Also, with the present invention the procedure isperformed through a system of guarded instrumentation, time is notwasted constantly placing and replacing various soft tissue retractorsthroughout the procedure.

5. Implant stability—Dislodgement of the implant would be a major sourceof device failure (an unsuccessful clinical result), and might result inpatient paralysis or even death. As discussed, the BAGBY device lacksany specific means of achieving stability and since it is pounded inagainst resistance to achieve vertebral distraction, and is susceptibleto forceful dislodgement by the tendency of the two distractedvertebrae, to return to their original positions squeezing out thedevice. The present invention, however, is screwed into place. As thereis no unscrewing force present between the vertebrae, compression alonecannot dislodge the implant. The implant is inherently stable by itsdesign. Furthermore, the threads of the present invention are highlyspecialized in that they are periodically interrupted so that the tailends of each of the tabs so formed are blunted and twisted so as toresist accidental unscrewing. The removal of an implant with such“locking threads” requires the use of a special extractor includedwithin the instrumentation. The stability of the present invention isstill further enhanced, again in contradistinction to the BAGBY device,by the presence of a “bone ingrowth” surface texturing, which bothincreases the friction of the fit and allows for the direct growth ofthe vertebral bone into the casing of the implant itself.

6. Spinal stability—The present invention is not only self-stabilizing,it also provides stability to the adjacent vertebrae in at least threeways that the BAGBY device cannot. First, the BAGBY device is placedtransversely across the joint in the center, leaving both vertebrae freeto rock back and forth over this round barrel shaped axis, much like aboard over a barrel, being used for a seesaw.

Secondly, as the BAGBY device lacks any specific design features toresist sliding, it may actually behave as a third body allowing thetranslation of the vertebrae relative to the device and to each other.

Thirdly, any device can only provide stability if it remains properly,seated. The present invention is inherently stable, and thereforeassures that it will stabilize the adjacent vertebrae, rather than, aswith the BAGBY, the instability of the spine to be treated may cause adislocation of the BAGBY implant, with further loss of spinal stability.

7. The collapse of the interspace—While both the present invention andthe BAGBY device can be fabricated to withstand the compression forceswithin the interspace, the interspace may nevertheless collapse underthe superincumbent body weight as the implant settles into the vertebralbone. This is related to the load per unit area. Again the presentinvention is superior to the BAGBY device in at least four ways.

First, the present invention offers considerably greater surface area todistribute the load. Secondly, while the BAGBY device is placedcentrally, the present device is placed bilaterally where the bone tendsto be more cortical and much stronger out towards the rim. Thirdly, thepresent invention supports the load achieving an “I” beam effect,whereas the BAGBY implant does not. Fourthly, it is not pressure alonethat causes the collapse of the bone adjacent to the implant, but alsobony erosion that is caused by the motion under pressure of the implantagainst the bone. As discussed in item 6 above, the present inventionalone is highly resistant to such motion, again diminishing thelikelihood of erosion and interspace collapse.

8. Bone ingrowth surface texturing—The present invention has a surfacetreatment of known and conventional technology to induce the growth ofbone from the vertebrae directly into the casing material of the implantitself. The BAGBY device has no similar feature. {L.A.—we may want tolist examples of these bone growth factors}

9. Fusion mass—The BAGBY invention calls for removing the disc and thendrilling a hole between the adjacent vertebrae. The bony debris sogenerated is then put into the device. The present invention takes acore of pure bone producing marrow from the iliac crest, and then by useof a special press, forcibly injects the implant device with anextremely dense compressed core of that osteogenic material until thematerial itself virtually extrudes from every cell of the implant.

10. The probability of achieving fusion—The fusion rate within the spineis known to be related directly to the amount of exposed vascular bonebed area, the quality and quantity of the fusion mass available, and theextent of the stabilization obtained with all other factors being halfconstant. It would then be anticipated, that the fusion rate would besuperior with the present invention as compared to the BAGBY device,because of optimal implant stability (#5), optimal spinal stability(#6), bone ingrowth surface treatment (#8), superior fusion mass (#9),and the greater exposed vertebral bony surface area (#7).

The last area of prior art possibly related to the present invention andtherefore, to be considered related to “bony ingrowth”, are patents thateither describe methods of producing materials and or materials ordevices to achieve the same. Such patents would include:

U.S. Pat. No. 4,636,526 (DORMAN), U.S. Pat. No. 4,634,720 (DORMAN), U.S.Pat. No. 4,542,539 (ROWE), U.S. Pat. No. 4,405,319 (COSENTINO), U.S.Pat. No. 4,439,152 (SMALL), U.S. Pat. No. 4,168,326 (BROEMER), U.S. Pat.No. 4,535,485 (ASHMAN), U.S. Pat. No. 3,987,499 (SCHARBACH), U.S. Pat.No. 3,605,123 (HAHN), U.S. Pat. No. 4,655,777 (DUNN), U.S. Pat. No.4,645,503 (LIN), U.S. Pat. No. 4,547,390 (ASHMAN), U.S. Pat. No.4,608,052 (VAN KAMPEN), U.S. Pat. No. 4,698,375 (DORMAN), U.S. Pat. No.4,661,536 (DORMAN), U.S. Pat. No. 3,952,334 (BOKROS), U.S. Pat. No.3,905,047 (LONG), U.S. Pat. No. 4,693,721 (DUCHEYNE), U.S. Pat. No.4,070,514 (ENTHERLY).

However, while the implant of the present invention would utilize boneingrowth technology, it would do so with conventional technology.

b. Prior Art Instrumentations and Methods

The following is a history of the prior art apparatus and methods ofinserting spinal implants:

In 1956, Ralph Cloward developed a method and instruments which he laterdescribed for preparing the anterior aspect (front) of the cervicalspine, and then fusing it. Cloward surgically removed the disc to befused across and then placed a rigid drill guide with a large foot plateand prongs down over an aligner rod and embedded said prongs into theadjacent vertebrae to maintain the alignment so as to facilitate thereaming out of the bone adjacent the disc spaces. As the large footplate sat against the front of the spine, it also served as a fixedreference point to control the depth of drilling. The reaming left twoopposed resected arcs, one each, from the opposed vertebral surfaces.The tubular drill guide, which was placed only preliminary to thedrilling, was thereafter completely removed. A cylindrical bony dowel,significantly larger in diameter than the hole formed, was then poundedinto the hole already drilled. Cloward's method of instrumentation wasdesigned for, and limited to, use on the anterior aspect and in theregion of the cervical spine only. The hole was midline, which wouldpreclude its use posteriorly where the spinal cord would be in the way.

As the bone graft to be inserted in Cloward's method was necessarilylarger in diameter than the hole drilled, the graft could not beinserted through the drill guide. This mandated the removal of the drillguide and left the graft insertion phase completely unprotected. ThusCloward's method and instrumentation was inappropriate for posteriorapplication.

In addition, the failure to provide continuous protection to thedelicate neural structures from the instruments, as well as the bony andcartilaginous debris generated during the procedure, made Cloward'smethod inappropriate for posterior application. Also, the drill guidedescribed by Cloward could not be placed posteriorly within the spinalcanal, as the foot plate would crush the nerves. Modifying Cloward'sdrill guide by removing the foot plate completely, would still leave theinstrument unworkable as it would then lack stability, and would not becontrollable for depth of seating.

Nevertheless, Wilterberger, (Wilterberger, B. R., Abbott, K. H., “DowelIntervertebral Fusion as Used in Lumbar Disc Surgery,” The Journal ofBone and Joint Surgery, Volume 39A, pg. 234-292, 1957) described theunprotected drilling of a hole from the posterior into the lumbar spinebetween the nerve roots and across the disc space, and then inserting astack of button-like dowels into that space. While Wilterberger hadtaken the Cloward concept of circular drilling and dowel fusion andapplied it to the lumbar spine from a posterior approach, he had notprovided for an improved method, nor had he advanced the instrumentationso as to make that procedure sufficiently safe, and it rapidly fell intodisrepute.

Crock (Crock, H. V., “Anterior Lumbar Interbody Fusion—Indications forits Use and notes on Surgical Technique,” Clinical Orthopedics, Volume165, pg. 157-163, 1981) described his technique and instrumentation forAnterior Interbody Fusion of the lumbar spine, wherein he drilled twolarge holes side by side across the disc space from anterior toposterior essentially unprotected and then pounded in two at leastpartially cylindrical grafts larger than the holes prepared.

A review of the prior art is instructive as to a number of significantdeficiencies in regard to the method and instrumentation for theperformance of Interbody Spinal Fusion utilizing drilling to prepare theendplates.

As the great majority of spinal surgery is performed in the lumbar spineand from posteriorly, a review of the prior art reveals a number ofdeficiencies in regard to the spine in general, and to the posteriorapproach to the lumbar spine specifically. These deficiencies includethe:

1. Failure to protect the surrounding tissues throughout the procedure,specifically, prior to drilling and until after the insertion of thegraft;

2. Failure to contain the debris, bony and cartilaginous, generatedduring the procedure;

3. Failure to optimize the contact of the cylindrical drill hole andbone graft, the mismatch in their diameters resulting in incongruence offit;

4. Failure to determine the optimal drill size prior to drilling;

5. Failure to determine the optimal amount of distraction prior todrilling;

6. Inability to optimize the amount of distraction so as to restore thenormal spatial relationships between adjacent vertebrae;

7. Inability to create sufficient working space within the spinal canal(between the nerve roots and the dural sac) to make the procedure safe;

8. Absent a foot plate on the drill guide, as necessitated by the closetolerances posteriorly, the inability to reliably insure that thedrilling is parallel to the vertebral endplates;

9. The inability to insure equal bone removal from the opposed vertebralsurfaces; and

10. The inability to determine within the spinal canal, the proper sideby side positioning for dual drill holes.

BRIEF SUMMARY OF THE INVENTION

The present invention comprises a series of artificial implants, thepurpose of which is to participate in, and directly cause bone fusionacross an intervertebral space following the excision of a damaged disc.Such implants are structurally load bearing devices, stronger than bone,capable of withstanding the substantial forces generated within thespinal interspace. The devices of the present invention have a pluralityof macro sized cells and openings, which can be loaded with fusionpromoting materials, such as autogenous bone, for the purpose ofmaterially influencing the adjacent vertebrae to perform a bony bond tothe implants and to each other. The implant casing may be surfacetextured or otherwise treated by any of a number of known technologiesto achieve a “bone ingrowth surface” to further enhance the stability ofthe implant and to expedite the fusion.

The devices of the present invention are configured and designed so asto promote their own stability within the vertebral interspace and toresist being dislodged, and furthermore, to stabilize the adjacentspinal segments.

The apparatus and method of the present invention for preparing thevertebrae for insertion of the implant allows for the rapid and saferemoval of the disc, preparation of the vertebrae, performance of thefusion, and internal stabilization of the spinal segment.

The present invention is a method for Interbody Spinal Fusion utilizingnovel instrumentation, whereby a protective tubular member, or pairedtubular members are placed prior to the drilling part of the procedureand may be left in place until the implant is fully seated.

By way of example, regarding the posterior approach to the lumbar spine,two distractors are used to separate two adjacent vertebrae to apreferred distance. A hollow Outer Sleeve having teeth at one end isdriven into the adjacent vertebrae on one side to hold the vertebrae inposition when the distractor is removed, a diameter reducing hollowInner Sleeve is introduced into the Outer Sleeve, a drill having a drillstop is passed through the hollow Inner Sleeve to drill a hole to adesired depth, and an implant is inserted in the hole. The method isrepeated on the other side of the disc.

The present invention provides apparatus and method of inserting spinalimplants from the anterior, posterior and lateral aspect of the spine.The instrumentation and method of the present invention provides adistractor instrument configured to restore and maintain the normalangular relationship of the vertebrae of the spine, known as lordosis orkyphosis, prior to the completion of the fusion procedure. The presentinvention also provides an extended outer sleeve that is a combinationdistractor and outer sleeve used for performing the surgical procedureof the present invention. The combination distractor and outer sleevemay also be configured to maintain the normal angular relationship ofthe vertebrae during the surgical procedure. The present inventionfurther discloses a combination distractor outer sleeve that may be usedto perform the surgical procedure of the present invention from thelateral aspect of the spinal column that protects the great vessels andneural structures from being damaged during the surgical procedure.

In summary then, the present invention, instrumentation, and method,provides for the performance of a total nuclear discectomy, an interbodyfusion, a rigid internal fixation of the spine as a single integratedsurgical procedure.

Discussion of the Instrumentation

The apparatus and method of the present, invention provide the followingadvantages:

1. The present invention is safer by providing protection of thesurrounding tissues. An Outer Sleeve places all of the delicate softtissue structures, nerves, blood vessels, and organs outside of the pathof the various sharp surgical instruments and the implant. Further, itis an improvement upon hand held retractors in that it occupies theleast possible amount of area, avoids the stretching associated withmanual retraction, provides for the retraction and shielding of thesurrounding tissues in all directions circumferentially andsimultaneously, and it does so exclusively with smooth, curved surfaces.

2. The present invention is safer by providing protection against thedanger of instrument or implant overpenetration.

3. The present invention is safer as the surgical site and wound areprotected from the debris generated during the procedure.

4. The present invention is safer because the method provides forabsolute protection to the soft tissues directly and from indirectinjury by overpenetration. It makes safe the use of powerinstrumentation which is both more effective and efficient.

5. The present invention maintains the vertebrae to be fused rigidthroughout the procedure.

6. The present invention holds the vertebrae to be fused alignedthroughout the procedure.

7. The present invention holds the vertebrae to be fused distractedthroughout the procedure.

8. The present invention assures that all instruments introduced throughthe Outer Sleeve are coaxial and equally centered through the disc spaceand parallel the endplates.

9. The present invention facilitates the implant insertion bycountering, the high compressive forces tending to collapse theinterspace, which if left unchecked would resist the introduction andadvancement of the implant and make stripping more likely.

10. The present invention extends the range and use of the procedure andsimilarly the interbody spinal implant itself by making the proceduresafe throughout the spine.

11. The present invention increases the ability to use a specificallysized implant.

12. In the present invention the end of all the penetratinginstrumentation is blunt faced.

13. In the present invention all of the instruments have been stopped ata predetermined depth to avoid overpenetration.

14. The design of the Outer Sleeve in the present invention conforms tothe spacial limitations of the specific surgical site.

15. The design and use of a second or Inner Sleeve in the presentinvention allows for the difference in size between the inside diameterof the Outer Sleeve, and the outside diameter of the drill itself. Thisdifference being necessary to accommodate the sum of the distraction tobe produced, and the depth of the circumferential threading present ofthe implant.

16. In the present invention a specially designed drill bit with acentral shaft recess allows for the safe collection of the drillingproducts, which can then be removed without disturbing the Outer Sleeveby removing the drill bit and Inner Sleeve as a single unit.

17. In the present invention a specially designed trephine is providedfor preparing cylindrical holes across the disc space and into twoadjacent vertebrae, and for harvesting of the bone graft by removing acore of bone slightly smaller in diameter than the internal diameter ofthe implant cavity itself, however of a greater length.

18. In the present invention a specially designed press for forcefullycompressing and injecting the long core of autogenous bone into theimplant, such that it extrudes through the implant itself.

19. In the present invention a specially designed driver extractor,which attaches to the implant and allows the implant to be eitherinserted or removed without itself dissociating from the implant, exceptby the deliberate disengagement of the operator.

20. In the present invention predistraction increases the working space.

21. The Distractor in the present invention is self-orienting acting asa directional finder.

22. The Distractor in the present invention is self-centralizing betweenthe opposed vertebral surfaces acting as a centering post for thesubsequent bone removal.

23. In the present invention predistraction assures the equal removal ofbone from the adjacent vertebral surfaces.

24. In the present invention predistraction assures the exact congruencebetween the hole drilled and the device.

25. In the present invention predistraction assures that the drilling isparallel to the vertebral endplates.

26. In the present invention predistraction allows for the determinationof the optimal distraction prior to drilling.

27. In the present invention predistraction allows for the verificationof the correct prosthesis size prior to drilling.

28. In the present invention predistraction facilitates device insertionby relieving the compressive loads across the interspace which wouldresist implantation.

29. In the present invention predistraction decreases the likelihood ofstripping the bone during insertion.

30. In the present invention predistraction provides for the side byside positioning, spacing, and parallelism required prior to theirrevocable event of drilling:

31. In the present invention predistraction provides for the rigidstabilization of the vertebrae opposed to the disc space throughout thesurgical procedure.

32. In the present invention predistraction provides for an implanteasier to insert as the compressive loads of the opposed vertebrae areheld in check so that the device itself need not drive the vertebraeapart to be inserted.

33. In the present invention predistraction allows for the insertion ofa more effective implant as more of the implant can be dedicated to itsintended purpose and be full diameter, whereas without the benefit ofpredistraction and the ability to maintain the same, a significantportion of the forward end of the implant would need to be dedicated tothe purpose of separating the opposing vertebrae.

34. The present invention allows for the use of an implant with asharper thread or surface projections as there is no danger to thesurrounding tissues.

35. The present invention allows for the implant to be fully preloadedas provided to the surgeon, or for the surgeon to load it with thematerial of his choice at the time of surgery.

36. The present invention allows for the loading of a spinal implantoutside of the spinal canal and prior to implantation.

37. The present invention provides for Distractors for the restorationof the physiologic amount of lordosis/kyphosis at any given level of thespine.

38. The Distractors of the present invention provide for the restorationof sagittal spinal alignment and the segmental correction of scoliosis.

39. The present invention provides Extended Outer Sleeves which are acombined Distractor and Outer Sleeve for the three dimensional segmentalrestoration of spinal alignment.

OBJECTS OF THE PRESENT INVENTION

It is an object of the present invention to provide an improved methodof performing a discectomy, a fusion, and an internal stabilization ofthe spine, and specifically, all three of the above simultaneously andas a single procedure.

It is another object of the present invention to provide an improvedmethod of performing a discectomy, a fusion, and an internalstabilization of the spine, which is both quicker and safer than ispossible by previous methods.

It is another object of the present invention to provide an improvedmethod of performing a discectomy, a fusion and an internalstabilization of the spine, to provide for improved surgical spinalimplants.

It is another object of the present invention to provide an improvedmethod of performing a discectomy, a fusion, and an internalstabilization of the spine, which provides for an improved system ofsurgical instrumentation to facilitate the performance of the combineddiscectomy, fusion, and internal spinal stabilization.

It is another object of the present invention to provide an improvedmethod of performing a discectomy, a fusion, and an internalstabilization of the spine.

It is an object of the present invention to provide instrumentation anda method of spinal interbody arthrodesis that is faster, safer, and moreefficacious than prior methods, and can effectively be performed in thecervical, thoracic, and lumbar spine anteriorly, as well as in the lowerlumbar spine posteriorly.

It is a further object of the present invention to provide a means forinserting a spinal implant between adjacent vertebrae while maintainingtheir optimal spacing, positioning, and alignment.

It is another object of the present invention to provide instrumentationfor restoring and maintaining the normal angular relationship ofadjacent vertebrae of the spine, be it lordosis, kyphosis, and/or thesegmental correction of scoliosis, achieving a total nuclear discectomy,an interbody spinal fusion, and a rigid internal fixation of a segmentof the spine as a single integrated surgical procedure for spinalfusion.

It is another object of the present invention to provide for aninstrument that is a combination Outer Sleeve and Distractor forinserting a spinal implant between adjacent vertebrae while effectingand maintaining the optimal, spacing, positioning, and alignment of thevertebrae.

It is another object of the present invention to provide a Distractorcapable of restoring and maintaining the normal angular relationshipbetween adjacent vertebrae that may be inserted within the disc spacebetween two adjacent vertebrae.

It is yet another object of the present invention to provideinstrumentation and a method of spinal interbody arthrodesis that isfaster, safer, and more efficacious than prior methods, and caneffectively be performed in the cervical, thoracic, and lumbar spine.

These and other objects of the present invention will be apparent fromreview of the following specification and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of the Long Distractor, of the presentinvention inserted into the intervertebral space.

FIG. 2 is a side elevational view of a Convertible Distractor assemblyin relation to the spine.

FIG. 3 is a perspective view of a high retention Short Distractor ofFIG. 2.

FIG. 3A is a side elevational view of the high retention ShortDistractor of FIG. 3.

FIG. 3B is a side elevational view of an alternative Short Distractorwith circumferential forward facing ratchetings.

FIG. 3C is a top view of the alternative Short Distractor of FIG. 3B.

FIG. 3D is a perspective view of an alternative embodiment of a ShortDistractor.

FIG. 3E is a top view of the alternative distractor of FIG. 3D.

FIG. 3F is a side elevational view of a further alternativerectangularized Short Distractor with knurled surfaces.

FIG. 4 is a perspective view of a spinal segment (two vertebrae and aninterposed disc) with a Short Distractor in place, with a portion of theupper vertebrae and disc cut away to show the Short Distractor on oneside of the spine and the Long Distractor about to be placedcontralaterally.

FIG. 5 is a side elevational view of the Outer Sleeve in place over theLong Distractor, and about to receive the Driver Cap in preparation forbeing seated.

FIG. 6 is a side elevational view of the Long Distractor, Outer Sleeve,and Driver Cap following the proper seating of the Outer Sleeve into thetwo adjacent vertebrae.

FIG. 7A is a side elevational view of the cervical Outer Sleeve beingplaced over a Long Distractor which is in place within the disc spaceanteriorly.

FIG. 7B is a bottom plan view of the single Outer Sleeve of FIG. 7A.

FIG. 7C is a bottom plan view of a Dual Outer Sleeve.

FIG. 7D is a side elevational view of the proximal portion of FIG. 7C.

FIG. 7E is a bottom plan view of a Dual Driver Cap for driving twodistractors.

FIG. 7F is a side sectional view showing the Dual Outer Sleeve of FIGS.7C and 7D, Distractors and Dual Cap of FIG. 7E seated in relation to thevertebrae.

FIG. 8 is a side elevational view of the Outer Sleeve of FIG. 7Acentered on the Long Distractor and fully seated on the anterior aspectof the cervical spine.

FIG. 9 is a perspective side view of the Distractor Puller.

FIG. 10 is a side elevational view of the Proximal Puller engaging theextraction ring of the Long Distractor shown in hidden line over the endof the Outer Sleeve.

FIG. 10A is a partial side elevational view of the Proximal Pullercoupled to the Long Distractor just prior to its extraction.

FIG. 10B is a posterior view of the proximal Outer Sleeve and a ShortDistractor shown in hidden line in place in regard to the vertebrae,disc and nerves.

FIG. 11A is a side sectional view of the Drill and Inner Sleeve withinthe Outer Sleeve drilling across the intervertebral space and cuttingpartially cylindrical arcs from the adjacent vertebrae.

FIG. 11B is a side elevational view of preparation of the intervertebralspace by the alternative “Trephine Method” showing the Distractor,Trephine, Inner Sleeve, and Outer Sleeve in place.

FIG. 11C is a side elevational view as in FIG. 11A, but showing the useof an alternative drilling conformation wherein the extended proximalportion of the Drill is both distracting and self-centering.

FIG. 11D is a side perspective view of an instrument for removing arcsof bone from vertebrae following drilling.

FIG. 12 is a side perspective view of the surgical Tap.

FIG. 13 is a partial sectional side view of the Outer Sleeve and thesurgical Tap fully threaded within the interspace.

FIG. 14A is a side elevational view of the bone harvesting Trephine andmotor adapter.

FIG. 14B is a perspective side view of the implant Bone Loading Device.

FIG. 14C is a perspective side view of the Corkscrew bone freeing andextracting instrument.

FIG. 15 is a perspective side view of the Bone Loading Device inoperation.

FIG. 16 is a partial sectional perspective side view of the ImplantDriver about to engage the spinal implant.

FIG. 17 is a partial sectional side elevational view of the spinalimplant being fully seated within the intervertebral space by means ofthe Driver apparatus in place within the Outer Sleeve.

FIG. 18 is a side elevational view of the lumbar spine showing the endresult of the spinal implant implantation via the posterior route.

FIG. 19 is a side elevational view of a Posterior Long LordoticDistractor inserted from the posterior aspect of the spine betweenadjacent vertebrae to restore and maintain lordosis of the spine.

FIG. 20 is a side elevational view of the Posterior Long LordoticDistractor shown partially in hidden line with the Outer Sleeve and Cap,inserted between adjacent vertebrae to restore and maintain lordosis ofthe spine with the Outer Sleeve engaging the vertebrae and properlyseated over the Posterior Long Lordotic Distractor.

FIG. 21 is a side elevational view partially in cross section of aspinal implant being inserted through an Outer Sleeve between twoadjacent vertebrae of the spine in which lordosis has been restored andmaintained and in which a portion of bone has been removed from eachvertebrae for receiving the spinal fusion implant.

FIG. 22 is a side elevational view of a spinal implant inserted betweentwo adjacent vertebrae of the spine in which lordosis has been restored.

FIG. 23 is a side elevational view of a Posterior Short LordoticDistractor of the present invention.

FIG. 24 is a top plan view along lines 24 - - - 24 of FIG. 23 of thePosterior Short Lordotic Distractor of the present invention.

FIG. 25 is a side elevational view of an Anterior Long LordoticDistractor of the present invention shown inserted between two adjacentvertebrae from the anterior aspect of the spine to restore and maintainlordosis.

FIG. 26 is a perspective side view of the Extended Outer Sleeve of thepresent invention having extended members for insertion within the discspace and engaging means for engaging adjacent vertebrae of the spine.

FIG. 27 is a side elevational view of the Extended Outer Sleeve of FIG.26 shown inserted between adjacent vertebrae of the spine.

FIG. 28 is an alternative embodiment of the Extended Outer Sleeve ofFIG. 26 shown without an engaging means for engaging adjacent vertebrae.

FIG. 29 is a perspective side view of a Posterior Lordotic ExtendedOuter Sleeve of the present invention having uneven extended members forrestoring and maintaining lordosis of the spine and engagement means forengaging the vertebrae.

FIG. 30 is a side elevational view of a portion of the PosteriorLordotic Extended Outer Sleeve of FIG. 29 inserted between adjacentvertebrae from the posterior aspect of the spine to restore and maintainlordosis.

FIG. 31 is a perspective side view of an Anterior Lordotic ExtendedOuter Sleeve of the present invention having extended members forrestoring and maintaining lordosis of the spine from the anterior aspectof the spine.

FIG. 32 is a side elevational side view of an alternative embodiment ofthe Anterior Lordotic Extended Outer Sleeve of FIG. 31 absent theengagement means for engaging the vertebrae, inserted between adjacentvertebrae from the anterior aspect of the spine.

FIG. 33 is a perspective side view of a Dual Extended Outer Sleevehaving an uneven extended portion which decreases in height in thedirection of insertion.

FIG. 34 is bottom plan view of the foot plate of the Dual Extended OuterSleeve of FIG. 33.

FIG. 35 is a perspective side view of a Dual Extended Outer Sleevehaving uneven extended portions which decrease in height in thedirection insertion.

FIG. 36 is an elevational front view of the apparatus of the presentinvention for use in installing interbody spinal implants having one ormore flat sides, shown placed over two Long Distractors with the prongsinserted into the vertebrae.

FIG. 37 is a bottom plan view of the foot plate of the apparatus of thepresent invention for use in installing the interbody spinal implantshaving one or more flat sides.

FIG. 38 is a cross sectional view along line 38-38 of FIG. 36illustrating the apparatus used for inserting interbody spinal implantshaving one or more flat sides.

FIG. 39 is a partial fragmentary view of the apparatus of the presentinvention for use in installing interbody spinal implants having one ormore flat sides, shown with the prongs being partially inserted into thevertebrae.

FIG. 40 illustrates a step of the method of drilling a hole into avertebrae with the apparatus of the present invention for use ininstalling interbody spinal implants having one or more flat sides,shown engaged to two adjacent vertebrae of a spinal column.

FIG. 41 illustrates a step of the method of the present invention forinserting a second interbody spinal implant having one or more flatsides into the interspace between two adjacent vertebrae with oneimplant shown already installed in place.

DETAILED DESCRIPTION OF THE DRAWINGS AND DETAILED DESCRIPTION OF METHODOF INSERTION

The following discussion will be in regard to application in the lumbarspine via the posterior approach. In its simplest form, the method ofthe present invention involves the following steps. The patient isplaced on a spinal surgery frame, which allows for the distraction andalignment of the disc space to be fused. A bilateral posterior exposureof the interspace, with or without partial discectomy is then performed.Utilizing distractors the disc space is distracted, and a hollow OuterSleeve is fitted over one of the distractors. The end of the OuterSleeve has engagement means, such as teeth, for engaging the twoadjacent vertebrae. The Outer Sleeve is driven into the vertebrae andthe distractor is then removed. A hollow Inner Sleeve is then insertedinto the Outer Sleeve and a stopped Drill is utilized to prepare theopposed vertebral surfaces. The Drill and the Inner Sleeve are removedas a single unit. The spate is tapped if so required. The preparedspinal implant is then inserted via the Outer Sleeve utilizing a stoppedinserter. The instruments are then removed and the procedure repeated onthe contralateral side of the spine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Step 1a. Prior to surgery, translucent implant templates appropriatelyadjusted for scale are superimposed on AP, lateral, and axial images ofthe interspace to be fused, for the purpose of selecting the optimalimplant size and to determine the desired distraction.

Step 1b. The patient is preferably placed onto a spinal surgery framecapable of inducing both distraction and vertebral alignment.

Step 2. In the preferred embodiment, a standard bilateral (partial)discectomy is performed and any posterior lipping of the vertebralbodies adjacent the interspace is removed. Alternatively, no discmaterial need be removed. In the preferred embodiment, the interspace isexposed by performing bilateral paired semihemilaminotomies andresecting the inner aspects of the facet joints adjacent the spinalcanal while preserving the supra and interspinous ligaments.

Step 3. Beginning on the first side, the dural sac and traversing nerveroot at that level are retracted medially and a Long Distractor theninserted and impacted flush to the posterior vertebral bodies adjacentthat interspace. Long Distractors with working ends of increasingdiameter are then sequentially inserted until the optimal distraction isobtained. This optimal distraction not only restores the normal heightof the interspace, but further achieves a balance wherein the tendencyfor the space to collapse is resisted, which in urging the vertebralbodies apart is being equally resisted by the powerful soft tissuestructures about the spinal segment including the outer casing of thedisc (the annulus fibrosus), various ligaments, capsular structures, aswell as the muscles and other soft tissue structures. This balanceddistraction not only provides for the spatial restoration of the heightof the interspace, but for considerable stability as the space nowresists further distraction or collapse.

In the preferred embodiment, as the desired distraction is approached,the use of the solid bodied Long Distractors is terminated and adisassembiable Convertible Distractor is placed with tactile and/orradiographic confirmation of ideal distraction. The ConvertibleDistractor is then disassembled such that the Short Distractor portionis left in place and the ultra-low profile head portion being positionedadjacent to the canal floor and safely away from the neural structures.To insure that the Short Distractor retains in place until its removalis desired, various embodiments of the Short Distractor are availablewith varying degrees of resistance to dislodgment. In the preferredembodiment of the procedure, attention is then directed to thecontralateral side of the spine.

Step 4. On the contralateral side of the same interspace the LongDistractor having at its working end the diameter matching the ShortDistractor already in place, is then inserted. If however, due to anasymmetrical collapse of the interspace if it is then determined thatgreater distraction is required on the second side to achieve theoptimal stability, then the appropriate Short Distractor would be placedon the second side. Then the Short Distractor would be removed from thefirst side and replaced with a larger Long Distractor so as to bring theinterspace into balance.

In an alternative embodiment, the entire procedure is performed on theone side of the spine utilizing only the Long Distractor prior torepeating the procedure on the contralateral side of the spine. Whilethis method can be performed in accordance with the remaining steps asdescribed in the preferred embodiment, when utilized it is bestperformed using a Trephine which allows the Long Distractor to remain inplace, thereby allowing for interspace distraction otherwise provided inthe first method by the Short Distractor. This alternative method thenrequires the use of a Trephine over the Long Distractor in lieu of areamer and is therefore called the “Trephine Method”, which will bediscussed in detail later.

Step 5. With the Short Distractor in place on the first side of thespine, and the matching Long Distractor in place on the second side ofthe spine, and with the dural sac and traversing nerve root safelyretracted, the Outer Sleeve is placed over the Long Distractor andfirmly impacted to its optimal depth using the Impaction Cap and amallet. The Long Distractor is then removed.

Step 6. An Inner Sleeve is then placed within the Outer Sleeve, and theinterspace is then prepared on that side by utilizing a boring meanssuch as, but not limited to, a Drill, Endmill, Reamer, or Trephine todrill, ream, or cut out the bone to be removed to either side, as wellas any remaining interposed discal material. In the preferred method,utilizing a specially designed Endmill-Drill, it and the Inner Sleeveare removed as a unit, safely carrying away the bone and disc debristrapped within them from the spinal canal.

Step 7. If required, a thread forming Tap with penetration limitingmeans to control the depth of insertion, is then inserted through theOuter Sleeve.

Step 8. The prepared implant is then inserted utilizing the specializedDriver unit. It should be noted that the implant may be coated with,and/or made of, and/or loaded with substances consistent with bonyfusion which may promote bone growth and/or fusion. However, in thepreferred embodiment, the implant is treated with bone promoting andinducing substances, but is loaded with materials suitable forparticipating in a fusion.

While substances both natural and artificial are covered by the presentinvention, the preferred embodiment is in regard to the use of thepatient's own bone by the following method. A hollow Trephine isutilized to harvest a core of bone from the posterior superior aspect ofthe iliac crest adjacent the sacroiliac joint. This core of bone is atits outside diameter, slightly smaller than the inside diameter of thespinal implant to be loaded, but longer than the spinal implant.Utilizing an instrument designed for that purpose, the core of bone isthen injected from within the Trephine into the central cavity of theimplant causing a superabundance of the bone material within the implantsuch that the bone material tends to press out through the openingscommunicating with the outside surface of the implant.

Step 9. Using the Driver Extractor instrument, the prepared implant isthreaded into the prepared interspace. The instrumentation is removedfrom that side of the spine and attention is then redirected to thefirst side of the spine. A small retractor is utilized to move the duralsac and traversing nerve root medially and to protect them and allowingthe direct visualization of the retained Short Distractor unit. Withoutremoving the Short Distractor, it is reassembled to its shaft portion,essentially reconstituting itself into a Long Distractor. With theinserted implant now acting as the distractor on the opposite side, theLong Distractor is utilized to guide the Outer Sleeve down where it isimpacted as described in Step 5.

Steps 6 & 7 are then repeated, completing the procedure at that level.The wound is then irrigated and closed in the routine manner.

Representative Example of The Preferred Method

Through preoperative templating of the patient's anterior posterior,lateral, and axially imaged MRI scan in conjunction with translucentoverlays of the various sized implants, the correct implant diameter andlength are accurately assessed, as well as the correct amount ofdistraction needed to restore the interspace to its premorbid height.The patient is then properly positioned and a bilateral partialdiscectomy performed via paired semihemilaminotomies.

For the purpose of this example, it will be assumed that by preoperativeassessment it was determined that the correct implant would have anexternal diameter of 18 mm and be 26 mm long. Further, the distractionnecessary to restore the height of the interspace would be approximately10 mm. The dural sac and traversing nerve root would then be retractedmedially and protected, while a Long Distractor having an outsidediameter at the barrel portion corresponding to the implant to beinserted, that is 18 mm, and having a diameter at the working end ofperhaps 8 mm, would be inserted. This then being found to be slightlysmaller than optimal by direct observation, a Convertible Distractorhaving in its barrel portion an 18 mm outside diameter, but having inits working portion a 10 mm diameter would then be inserted. Directobservation and/or x-ray then confirming the ideal distraction, theConvertible Distractor would then be disassembled, the barrel and headportion removed, and the Short Distractor portion left deeply embeddedand with its flanged head flat against the canal floor and deep to theneural structures. It would then be safe to allow the dural sac andnerve root to return to their normal positions, which would besuperficial to the flanged portion of the Short Distractor.

Attention would then be directed to the contralateral side. The duralsac and nerve root would then be retracted medially on this second side,and a Long Distractor with an 18 mm diameter barrel portion and a 10 mmworking portion would then be inserted into the interspace and drivenflush to the bone if necessary, such impaction imploding any osteophytesnot already removed, and assuring that the shoulder portion of thebarrel comes to lie flat against the posterior aspects of the adjacentbodies. With the dural sac and nerve root still safely retracted, theOuter Sleeve would then be placed over the Long Distractor and utilizingthe Driver Cap and a mallet, seated to the optimal depth.

In the preferred embodiment, the Long Distractor is then removed and theInner Sleeve is inserted into the Outer Sleeve. Since the purpose of theInner Sleeve is to support the drill and allow for the increased size ofthe implant over the size of the drill, thus making it possible for theinsertion of the implant to occur through the Outer Sleeve, the InnerSleeve therefore measures 18 mm in its outside diameter, and 16.6 mm inits inside diameter. This allows it to fit within the Outer Sleeve, thediameter of which is 18.1 mm and to admit the drill bit which is 16.5 mmin diameter.

Following the drilling procedure, the Drill and Inner Sleeve are removedas a single unit with the trapped interposed cartilaginous and bonydebris. The depth of drill penetration is preset and limited by thefixed rigid column of the Outer Sleeve. In this example, the space willbe prepared to a depth of 28 mm in anticipation of countersinking a 26mm long implant at least 2 mm. If a Tap were to be utilized, it would beinserted at this time and be appropriate to the minor and majordiameters of the implant to be inserted and as with the Drill,controlled for its depth of penetration. The spinal implant would thenbe prepared for implantation by utilizing a Trephine to harvest a coreof posterior iliac bone greater than 30 mm long and approximately 14.5mm in diameter.

Using the Bone Loading Device, this core of bone would be forcefullyinjected into the internal chamber of the spinal implant which wouldthen be capped. Cap end forward, the fully loaded implant would then beattached to the Insertion Driver, down the Outer Sleeve and screwed intoplace with the depth of penetration limited by the Insertion Driver. TheInsertion Driver is then unscrewed from the implant and removed from theOuter Sleeve. With the dural sac and nerve root retracted and protected,the Outer Sleeve would then be removed. This would complete the fusionprocedure on that side, and then as described, the procedure would berepeated on the other (first) side of the same interspace.

Alternative Methods

An alternative and extremely useful method is the “Trephine Method”. Itsadvantages include that it may be used in conjunction with the preferredembodiment substituting the use of a hollow, tubular cutter, called aTrephine for the use of the Drill in Step 5 of the preferred embodiment.Additionally, it may be utilized so as to obviate the need for theplacement of the Short Distractor and to allow the procedure to beeffectively performed from start to finish on one side prior toinitiating the procedure on the opposite side, and while neverthelessmaintaining distraction at the site of the bone removal.

The following is a description of the “Trephine Method”. Havingcompleted the exposure of the interspace on at least one side, the duralsac and nerve root are retracted. A Long Distractor differing from theLong Solid Bodied Distractor of the preferred embodiment only in thatthe barrel portion is of a precisely lesser diameter than the spinalimplant. As in the preferred embodiment, the Outer Sleeve has an innerdiameter only slightly greater than the implant to be inserted.Therefore, at this time, a first Inner Sleeve is inserted into the OuterSleeve to make up the difference between the outside diameter of theLong Distractor and the inside diameter of the Outer Sleeve. With theOuter Sleeve and first Inner Sleeve thus assembled, they are placed overthe Long Distractor and the Outer Sleeve is optimally seated using theImpaction Cap. The Cap and first Inner Sleeve are removed, but the LongDistractor and Outer Sleeve are left in place.

With the Long Distractor maintaining optimal distraction and with theOuter Sleeve locking the vertebrae together so as to resist any movementof the vertebrae, a hollow, tubular cutter known as a Trephine is theninserted over the Long Distractor and its barrel portion and within theOuter Sleeve. The Trephine, which is stopped out to the appropriatedepth, can then be utilized to cut equal arcs of bone from the opposedvertebral endplates.

Alternatively, a second Inner Sleeve may be placed within the OuterSleeve prior to placing the Trephine over the Long Distractor and withinthat second sleeve. This second Inner Sleeve would be just greater inits internal diameter than the Long Distractor and just smaller in itsoutside diameter than the inner diameter of the Outer Sleeve. While itwould provide enhanced stability to the Trephine, provision would thenneed to be made in the way of large flutes passing longitudinally orobliquely along the outer surface of the Distractor to its barrelportion to accommodate the bony and cartilaginous debris generatedduring the cutting procedure.

Following the use of the Trephine to the appropriate depth by either ofthese methods, the Trephine, the Long Distractor, and the second InnerSleeve, if utilized, are all removed. Since the Trephine cuts two arcsof bone but does not ream them out, a shafted instrument with aperpendicular cutting portion at its working end is then insertedparallel to the disc space and then rotated through an arc of motioncutting the bases of the two longitudinally cut arcs, thus freeing themfor removal through the Outer Sleeve. The space may then be tapped ifrequired, and the implant is inserted as per the preferred method. Asalready mentioned, the “Trephine Method” can be used with or without theuse of the Short Distractor on the contralateral side.

Applications of Method in Other Areas of the Spine

The following method is the preferred embodiment for performing anteriorinterbody fusion in the thoracic and lumbar spines. It is alsoappropriate in the cervical spine when the width of the spine anteriorlyis sufficient so that it is possible to place two implants side by sideand such that each intrudes at least several millimeters into thesubstance of the opposed vertebrae and for the length of the implants.

The interspace to be fused is adequately exposed and the soft tissuesand vital structures retracted and protected to either side.Visualization of the broad width of the interspace anteriorly is madepossible by the absence of the neurological structures in relation tothis aspect of the spine. The center line of the anterior aspect of theinterspace is noted and marked. The disc is removed using first a knifeand then curettes and rongeurs as needed. Alternatively, the disc may beleft intact to be removed during the drilling stage of the procedure.However, as per the preferred embodiment of the procedure, havingremoved the great mass of the nucleus and the greater portion of theannulus anteriorly, Long Distractors with progressively increasingdiameters to their working ends are inserted into the interspace at apoint midway between the central marking line and the lateral extent ofthe anterior aspect of the spine as visualized.

The Dual Outer Sleeve with its common Foot Plate and Retention Prongs isthen inserted over either a singly placed Long Distractor and then thesecond Distractor placed, or is placed over both Distractors if alreadyplaced. The Dual Outer Sleeve is then seated firmly against the anterioraspect of the spine. Any spurs which would interfere with the flushseating of the Foot Plate to the anterior aspect of the spine should beremoved prior to inserting the Long Distractors. Once the Outer Sleevehas been optimally seated, one of the Long Distractors is removed and inits place is inserted an Inner Sleeve and drill bit. The drill bit hasas its outside diameter the minor diameter of the implant to beinserted. The Inner Sleeve is essentially equal in thickness to thedifference between the minor and major diameters of the threadedimplant.

A Stopped Drill is then utilized to prepare the opposed vertebralsurfaces and to remove any remaining disc material interposed. Ifrequired, a Stopped Tap may be inserted through the Outer Sleeve andinto the interspace to create a thread form. The properly preparedimplant is then affixed to the Insertion Driver and passed through theOuter Sleeve down into the interspace and inserted until its depth ofpenetration is limited by the stop on the Insertion Driver. With theimplant itself now in a position to act as a distractor, the LongDistractor is then removed from the contralateral side and the procedurerepeated. When both implants are firmly in place, the outer sleeve maythen be removed. The amount of countersinking of the implants may thenbe adjusted under direct vision.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Method andInstrumentation

In the preferred embodiment, the disc (D) between adjacent vertebrae (V)is approached via bilateral paired semihemilaminotomies of the adjacentvertebrae. In the preferred embodiment the supraspinous ligament, theinterspinous ligament, the spinous process, portions of the lamina, andmost of the facet joints are preserved. However, while less desirable,these structures may be removed.

In the preferred method, a bilateral partial nuclear discectomy is thenperformed through bilateral openings created through the posterioraspect of the annulus fibrosus. While considered less desirable, discexcision can be delayed and performed simultaneously with the vertebralbone resection during the drilling procedure. Starting on the firstside, a dural nerve root retractor is placed such that the dural sac andlower nerve root are retracted medially allowing exposure to one side ofa portion of two adjacent vertebral bodies and the interposed discposteriorly.

Referring now to FIG. 1, preferably after removing some portion ofnuclear disc material, a Long Distractor 100 is inserted under directvision into the intervertebral space. The disc penetrating portion 102is essentially cylindrical with a bullet-shaped front end 103 and ashoulder portion 104 where the penetrating portion 102 extends frombarrel 106. The penetrating portion 102 urges the vertebral bodiesapart, facilitating the introduction of the instruments. LongDistractors with sequentially increasing diameter penetrating portions102 are then introduced. As the optimal diameter of penetrating portion102 is achieved, the Vertebrae V to either side are forced into fullcongruence and thus become parallel, not only to the penetrating portion102, but to each other. At this time, any remaining excrescences of boneof the posterior vertebral bodies adjacent the posterior disc which havenot already been removed are flattened flush to the vertebral body bythe forced impaction, such as by hitting with a hammer flat surface 109of crown 110, driving the shoulder 104 against the lipped portions ofvertebrae V. Because of the forced opposition of the vertebral endplatesto portion 102 with optimal distraction, Long Distractor 100 will thencome to lie absolutely perpendicular to the plane of the posteriorbodies and absolutely parallel to the vertebral endplates, allowingoptimal alignment for the procedure to be performed.

Penetrating portion 102 is available in various diameters, but all areof a constant length, which is less than the known depth of theinterspace. This combined with the circumferential shoulder 104, whichis too large to fit within the interspace, protects against the dangerof overpenetration. Barrel 106 is of the same diameter as the externaldiameter of the device to be implanted. A recessed portion 108 below thecrown 110 allows for the Long Distractor 100 to be engaged by anextractor unit shown in FIG. 9.

Referring to FIG. 2, in the preferred embodiment, a Convertible LongDistractor 113 is used on the first side of the spine. The ConvertibleLong Distractor 113 has a barrel portion 152 separable from the ShortDistractor portion 120. While the initial distraction may be performedwith a solid Long Distractor, as the optimal distraction is approachedthe appropriate Convertible Long Distractor is utilized. The ConvertibleLong Distractor 113 consists of a Short Distractor portion 120 and abarrel 152 having a rectangular projection 134 at one end. The ShortDistractor 120 has an increased diameter head 128, a rectangular slot118 and an internal threaded opening 114. The barrel 152 is hollow andhas an internal shaft 111 terminating in a large diameter hexagonalcrown 115 at one end and a reduced diameter portion 112. The crown 115has a detent portion 117 in its flat surface. The other end of the shaft111 has a threaded working end screw 116 that corresponds to threadedopening 114. The shaft 111 is prevented from removal from the barrel 152by set pin 119 passing through the wall of barrel 152 in a convenientmanner. The Short Distractor portion 120 is removably attached to thebarrel portion 152 via the mating of female rectangular slot 118 and themale mating member 134. The mating held together by utilizing knob 135to drive the crown 110 connected to interior shaft 111 having a threadedworking end screw 116 that threads into the female rectangular slot 118of the Short Distractor portion 120.

Knob 135 has an open socket 138 for fitting around crown 115 and engagesthe reduced diameter hexagonal portion 112 so as to permit the rotationof shaft 111 and threaded working end screw 116. A detent ball 150 inthe inside of the socket 138 engages detent 117 in the crown 115,holding them together.

Referring to FIGS. 2, 3, and 3A-3F the Short Distractor portion 120 aredesigned to provide for high stability when temporarily situated so asto resist inadvertent migration while the surgeon is working on thesecond side. To that end, the embodiment of the Short Distractor 120shown in FIGS. 3 and 3A, has a pair of sharp pegs 126, to embed into theopposing vertebral bodies and forward facing ratchetings 124, thatfurther resist backward movement. FIGS. 3B and 3C, which show thepreferred embodiment, are side and top views of an alternativeembodiment of the distractor portion such that the distractor portion tobe interposed between the vertebrae is essentially cylindrical, but withcircumferential forward facing ratchetings 124.

Referring to FIGS. 3D and 3E, a further alternative embodiment of theShort Distractor is shown. This is a more rectangularized design, withforward facing ratchetings, without the sharp prongs 126 of FIG. 3. FIG.3F is a side view of a further embodiment of the Short Distractor 120shown with knurling, to increase the interference with the bone surfaceso as to add stability to the unit and to resist dislodgment. To thisend, it is apparent that the working ends of both the Long and ShortDistractors can have a variety of configurations consistent with theirpurpose, and that surface irregularities as well as the shape of theends themselves, with or without prongs 126, may be utilized to make theShort Distractor 120 more resistant to migration.

Once the ideal distraction has been achieved on the first side of thespine, the Convertible Distractor is dissociated, leaving ShortDistractor 120 in place with its rounded external end 128, safely on thecanal floor and deep to the dural sac and nerve root.

Referring to FIG. 4, the surgeon then moves to the other side of thespine at the same disc (D) level, and retracts the dural sac and nerveroot medially, exposing the disc on that side. Long Distractors 100 arethen sequentially inserted into the disc space until the diameter of thedistractor on the second side is at least as big as that on the firstside. If because of some asymmetry of the interspace, a larger diameterdistractor is required on the second side to achieve the idealdistraction as compared to the first side, then the second side isfitted with a Short Distractor of the larger diameter, and the surgeonwould then return back to the first side. In that event, the first sideShort Distractor would then be removed and the Long Distractor 100corresponding to the increased diameter of the already placed ShortDistractor 120 would then be inserted. In either event, the operation iscontinued by working on the one side where the Long Distractor is inplace. In this regard, it should be noted, that by the use of such adevice as the Michelson Otrhopedic Support Frame, U.S. Pat. No.4,481,943 issued on Nov. 13, 1984, it may be possible to obtain adequatedistraction preoperatively such that the surgeon is either disinclinedto use a distractor, or to simply place the correct Long Distractor onthe first side and then proceed with the surgical procedure on that sidebefore moving to the opposite side. These variations are within thescope of the present invention.

Referring to FIG. 5, the Long Distractor 100 now serves as both acentering post and an alignment rod for the hollow Outer Sleeve 140which is fitted over the Long Distractor 100, shown by phantom lines101. The front end of the Outer Sleeve 140 is metal and has sharp teeth142 that are capable of penetrating into and holding fast the twoadjacent vertebrae (V). Interrupting the circumferential sharp teeth 142are flat, planar areas 152 which serve to resist the further insertionof the sharp teeth 142 into the vertebral bodies. The sharp teeth 142 ofthe Outer Sleeve 140 are a continuation of the tubular shaft 144, whichin turn is connected to circumferentially enlarged tubular back end 146having a knurled outer surface 148 for easier manipulation. Analternative embodiment of an Outer Sleeve incorporates an expansible keyhole and slot configuration 154 to either side of shaft 144 along themid-plane of the interspace and parallel to it such that the end 142resists the collapse of the vertebrae (V) to either side of the disc(D), but may nevertheless allow for their further distraction, in theevent the only diameter or the root diameter of the implant is largerthan the hole drilled.

A Driver Cap 160 in the form of an impaction cap has at its far end aflat, closed-back surface 162 and at its other end a broad, circularopening. The Driver Cap 160 fits over both the Outer Sleeve 140 and theLong Distractor 100. As the Driver Cap 160 is seated, interior surface170 circumferentially engages portion 146 of the Outer Sleeve until theback end 172 engages the internal shoulder 164. As mallet blows areapplied to surface 162, that force is transmitted via the internalshoulder 164 to the Outer Sleeve 140 via its far end 172, seating sharpteeth 142 into the vertebral bodies adjacent the disc space D and to thedepth of the teeth sharp 142 to the flat portions 152. As the OuterSleeve 140 is advanced forward, crown portion 110 of the Long Distractoris allowed to protrude within the Driver Cap 160 unobstructed until itcontacts the interior flat surface 168.

Referring to FIG. 6, once crown 110 comes into contact with the flatinterior surface 168, then further taps of the mallet will not advancethe Outer Sleeve, any further motion being resisted by the flat shoulderportion 104 of the Long Distractor abutting the hard surfaces of theposterior vertebral bodies. In this way, the Outer Sleeve 140 is safelyand assuredly inserted to its optimal depth and rigidly securing the twoopposed vertebrae as shown in FIG. 6.

Referring to FIG. 9, the Cap 160 is then removed and the DistractorPuller 200 of FIG. 9 utilized to remove the Long Distractor 100 from thespine leaving the Outer Sleeve 140 in place. The Distractor Puller 200has front portion 202, a mid portion 204, and a back handle portion 206.At the front portion 202 of the Distractor Puller 200, a socket 208 isconnected to one end of shaft 210 which at its far end is connected toback handle portion 206. The socket 208 has defined within it a cavity212 that is open at its front end and funnelized on the interior aspectof its sides. The cavity 212 is constructed so that the head of theDistractor Puller 200 and the partially circumferential flange 218engages the circumferential recess 108 of the Distractor 100. Theentrance to cavity 212 is slightly funnelized, and the leading edges offlange 218 slightly rounded to facilitate the engagement of recess 108and head 110 of Distractor 100, which is further facilitated in that theDriver Cap 160 leaves portion 108 of Distractor 100 precisely flush withthe back surface 172 of the Outer Sleeve 140. This provides a large,flat surface 172 to precisely guide surface 230 of socket 208, and openportion 212 around head 110 while flange 218 engages recess 108. Thespringloaded detent ball 228 engages hemispherical depression 112 in thecrown 110, shown in FIG. 2. This springloaded detent 228 in engagementwith complimentary indent 218 protects against the inadvertentdissociation of the Long Distractor from the Puller 200 after theDistractor has been removed from within the Outer Sleeve 140 and priorto its removal from the wound. Once out of the body, the two instrumentsare easily disassociated by freeing the crown portion 110 from cavity212 by a manual force applied perpendicular to their relative long axesat this location.

A cylindrical and free removable weight 216 is fitted around shaft 210between the front portion 202 and the rear handle portion 206. Gently,but repeatedly sliding the weight 216 along shaft 210 and drivenrearwardly against flat surface 228, transmits a rearward vector toproximal end 202 and thereby to the Long Distractor 100 to which it isengaged.

Paired extended handle 224 and 226, allow the surgeon to resist anyexcessive rearward motion as the instrument is used to liberate the LongDistractor 100. Paired handles 224 and 226 are also useful in that theyallow a rotational directing of portion 208, via the shaft 210. Thisallows the surgeon to control and manipulate rotationally theorientation of the opening of cavity 212 to facilitate its application,to the head 110 of the distractor 100.

The Distractor Puller 200 is a significant improvement over thealternatives of striking a remover instrument with an independent hammerover the exposed surgical wound, or manually extracting the distractorby forcefully pulling. The use of a free hammer over the open wound isdangerous because the neural structures can be impacted on the backswing which is made even more likely by the effects of gravity on themallet head. Manual extraction by pulling is dangerous because of thesignificant interference fit of portion 102 within the spine such thatsignificant force would be required to remove the Distractor 100, and ifforce were not coaxial then the Outer Sleeve might be dislodged ormisaligned. Further, once the flat portion 102 became free of theinterspace, all resistance to withdrawal would be lost and in the faceof the considerable force necessary to free it, the Distractor 100 mighteasily become projectile imparting injury to the patient and/or thesurgeon.

Once the Long Distractor 100 has been fully removed from the OuterSleeve 140, the toothed end 142 of the Outer Sleeve 140, working inconjunction with the Short Distractor 120 on the contralateral siderigidly maintains the relative position of the adjacent vertebrae V.Further, since the remainder of the procedure on that side of the spineoccurs entirely through the protective Outer Sleeve 140, and as thenerves and dural sac are external to that Outer Sleeve and superficialto the toothed end 142 of the Outer Sleeve 140, which is firmly embeddedinto the adjacent vertebrae V, the Outer Sleeve 140 serves to insure thesafety of these delicate neural structures. Further, since the OuterSleeve 140 is of a fixed length and rigid, its flat rearward surface 172may be used as a stop to the advancement of all instruments placedthrough the Outer Sleeve 140, thus protecting against accidentaloverpenetration. Further, the Outer Sleeve 140 assures that the furtherprocedure to be performed will occur coaxial to the disc space D andfurther, be symmetrical in regard to each of the opposed vertebralsurfaces.

Referring to FIG. 10B, a posterior view of the spine at this stage ofthe procedure, is shown with a Short Distractor 120 in place on one sideof the spine and the bottom portion of Outer Sleeve 140 in place on theopposite side of the spine.

Referring to FIG. 11A, an Inner Sleeve 242 is inserted from the rearwithin the Outer Sleeve 140. This Inner Sleeve has a collar portion 244of a known thickness which seats against the top edge surface 172 ofOuter Sleeve 140. The cylindrical barrel portion of Inner Sleeve 242comes to approximate the posterior aspect of the vertebral bodiesinterior the Outer Sleeve when fully seated. A Drill 240, having a knownselected length is then introduced through the rearward aperture of theInner Sleeve 242 and utilized to ream out the arcs of bone which itengages from the opposed vertebral endplates as well as any discalmaterial within its path down to its predetermined and limited depth.The Drill 240, has a narrow engagement portion 246, which allows it tobe affixed to a drill mechanism which may be either a manual or a powerunit. A circumferential collar 248 of an increased diameter serves tolimit the depth of penetration of the drill 240 and may be fixed, orlockably adjustable.

Not shown here, but well known to those skilled in the art, are variousmechanisms to lockably adjust such instruments as drills. Suchmechanisms include, but are not limited to, the use of collets, threadedshafts with lock nuts, and flanges engaging grooves forced therein byeither a cap pulled over the flanges or screwed down upon them.

In the preferred embodiment, the forward cutting edge 252 of Drill 240is a modification of a large fluted drill design such that the endresembles an end cutting mill which may contain any workable number ofcutting surfaces, but preferably four or more, and such cutting surfacesbeing relatively shallow such that the advancement of the instrumentoccurs more slowly. The outside diameter of the Drill 240 corresponds tothe minor diameter of the threaded spinal implant. The Inner Sleeve 242has an inner diameter slightly greater than that dimension and its outerdiameter is slightly smaller than the inside diameter of the OuterSleeve 140 which has the same outer diameter as the major diameter ofthe threaded implant.

The drill shaft of drill 240 comprises an upper portion 243, a centralrecessed portion 256 of a smaller-diameter and a lower cutting drillportion 250. The upper portion 243 and lower portion 256 of the drill240 have the same outside diameter.

The Inner Sleeve 242 serves many functions. First, it provides a moreintimate drill guide for drill 240 in the event a smaller diameter holeis to be drilled than that of the inside diameter of the Outer Sleeve140. Second, since it now guides the Drill, it allows for the OuterSleeve 140 to have an internal diameter large enough to admit thethreaded spinal implant, which is indeed considerably larger in diameterthan the Drill 240 itself.

If a larger Outer Sleeve 140 were utilized absent the Inner Sleeve 242,then the Drill 240 would be free to wander within the confines of thatgreater space and would not reliably make parallel cuts removing equalportions of bone from the adjacent vertebrae V. Further, the boneremoval not only needs to be equal, but must be correctly oriented inthree dimensions. That is, the path of the Drill 240 must be equallycentered within the disc space, parallel the endplates, and parallel tothe sagittal axis dissecting the interspace.

A further purpose of the Inner Sleeve 242 is that it may be removedsimultaneously with the Drill 240, thereby trapping the debris, bothcartilaginous and bony generated during the drilling procedure, whichare guided rearward by the large flutes 251 of Drill portion 250, wherethey are collected around recessed portion 256 between the recessedportion 256 and the inner wall of the Inner Sleeve 242 are therecontained therein. Thus, by removing the Drill 240 in conjunction withthe Inner Sleeve 242, all of the debris generated by the reamingprocedure is safely removed from the spinal canal and wound area.

Further, if the disc tissue in the area to be reamed has been removedpreviously, as per the preferred method, then the patient's own bone ofgood quality and useful within the operation will then be containedbetween the Inner Sleeve 242 and the shaft portion 256. Once away fromthe surgical wound, this material may be used to load the spinal implantor placed deep within the interspace to participate in the fusion.

The method of actually producing the surgical hole within the spine isvariable. As shown in FIG. 11C, in an alternative embodiment Drill end250 has a forward projecting nipple 260, which itself is bullet-shapedin its leading aspect so as to ease its entrance into the disc space andto urge the vertebrae apart. Nipple 260 is distracting, stabilizing asit resists any tendency of the vertebrae to move together, isself-centering to the Drill portion 250 when working in conjunction withSleeves 140 and 242, and virtually assures the symmetrical resection ofbone from the opposed vertebral surfaces.

Referring to FIG. 11B, the alternative “Trephine Method” referred toearlier in this application is shown. In this alternative, a LongDistractor 100 is left in place after the Outer Sleeve 140 is seated.The Long Distractor 100 in this case differs from the Long Distractor ofthe preferred embodiment in that its outside diameter of the barrel 106is of a smaller diameter than in the prior version. This is madenecessary because regardless of the method, the hole to be formedcorresponds to the minor diameter of the spinal implant. Trephine 270, ahollow, tubular member with sharp cutting teeth 251 at its proximal end,has a wall thickness and since the outside diameter of that trephine 270must correspond to the root diameter of the implant, then the wallthickness of the trephine 270 must be allowed for by a correspondingreduction in the diameter of the Long Distractor 100.

A further modification of the Long Distractor 100 to the “TrephineMethod” would use longitudinal grooves (not shown) along the barrelsurface 106 for the purpose of transmitting any debris generated duringthe cutting procedure, rearward. Since the cutting element is bothcentered and aligned by the Long Distractor, the use of the Inner Sleeve242 is not mandatory, but may once again be useful in controlling thepath of the debris. To that end, little debris is generated in the“Trephine Method” as the bony arcs are not so much being reamed out andremoved as they are simply being cut into the bone where these arcs ofbone are left connected at their far ends. Thus, when the TrephiningMethod has been completed and the Trephine 270 and Inner Sleeve 242removed, unlike in the preferred embodiment where the hole is drilledout, it remains necessary to remove both the two arcs of bone, and anyinterposed material. Nevertheless, this is very easily performed byvarious means, one of which is depicted in FIG. 11D.

Referring to FIG. 11D, Instrument 272 consisting of a shaft 276 attachedoff-center to the lower surface 273 handle 274 is shown. The shaft 274terminates in a cutting arm 278. The instrument 272 is inserted throughOuter Sleeve 140 where the lower surface 273 of handle 274 abuts the top172 of the Outer Sleeve 140, both stopping downward motion of instrument272 and precisely placing the perpendicularly cutting arm 278 ofinstrument 272 so that as handle portion 274 is rotated, the cutting arm278 is also rotated, cutting the arcs of bone and liberating them fromtheir last attachments. These portions of bone are then removedutilizing this instrument or a long forceps, and then placed within theimplants or otherwise used to participate in the fusion.

Referring to FIGS. 12 and 13, while in the preferred embodiment of thepresent invention the spinal implant I, is essentially self-tapping, ifthe bone is unusually hard it may be desirable to form the threadpattern within the interspace prior to the insertion of the implant I.To that end, as shown in FIG. 12, Tap 280 has a threadcutting portion282 connected by a shaft 286 to a handle portion 292, which has beendesigned to give mechanical advantage to the rotation of the instrumentfor the purpose of cutting threads. The lower portion of handle 290 hasa forward facing flat surface 288 too large to fit through the openingof Outer Sleeve 140 which thus safely limits the depth of penetration ofthe cutting element 282. This tap 280 is further made safe by blunt end294 which will engage the uncut portions of the vertebral bone justprior to the engagement of shoulder 288 against surface 172. Thisfeature allows the surgeon to appreciate a less harsh resistance as theblunt nose 294 encounters the remaining unresected bone for the drillhole and prior to the sudden increase in resistance caused by theseating of shoulder 288 against top edge 172, which first resistanceserves as a warning to the surgeon to discontinue the tapping procedure.Thus, the surgeon has both visual (as shoulder 288 approaches top edge172) and tactile warnings to avoid stripping the thread form. Tap end282 is highly specialized for its specific purpose. Rearward to thespecialized blunt tip 294 is a truncated bullet-shaped area 298 whichramps up to the constant diameter intermediate the cutting ridges 296.Ramp portion 298 urges the opposed vertebral bodies apart, which motionis resisted by Outer Sleeve 140, thus progressively driving the sharpleading edges of thread forms 296 into the vertebral bodies. Theperiodic longitudinal grooves 284 interrupting the thread forms, whichmay number 1 to 8, but preferably 4, function to accumulate the bonymaterial which is removed during the thread cutting process. In thatregard, in the ideal embodiment, the thread cutting form is designed tocompress the bone to be formed rather than to trough through it.Further, while both the major and minor diameters of the Tap 280 may bevaried, in the preferred embodiment, the minor diameter corresponds tothe minor diameter of the implant I, but the major diameter is slightlyless than the major diameter of the implant.

With Tap 280 now removed, and Sleeve 140 still in place, the surgicalsite is now fully prepared to receive the spinal implant I. In thepreferred embodiment of the spinal implant, the implant has beenenhanced by the use of, application to, and filling with fusionpromoting, enhancing, and participating substances and factors. Thus,the implant may be fully prepared for insertion as provided to theoperating surgeon. However, at the present time, human bone is mostcommonly used as the graft-material of choice, with the patient's ownbone being considered the best source.

Referring to FIG. 14A, a trephine 300 is shown with an exceedingly sharpfront cutting edge 302 for quickly and cleanly coring into the patient'sposterior iliac crest, or any other bony tissue, and for the purpose ofproducing a core of bone then contained within the hollow 304 of thetrephine 300. Trephine 300 has a rear portion 306 with a pair ofdiametrically opposed slots 310, and disposed clockwise from theirlongitudinally oriented rearward facing openings so as to engagediametrically and opposing members 312 of Drive unit 308, by whichtrephine 300 may be attached to either a hand or power drill. It can beappreciated that engagement mechanism 312 is stable during the clockwisecutting procedure, and yet allows for the rapid disconnection of the twocomponents once the cutting is completed.

Because of the high interference between the graft and the inner wall ofhollow portion 304, and the relative weakness of the cancellous bonebeing harvested, it is possible to remove the Trephine 300 while stilldrilling, and, to have it extract the core of bone with it. However, inthe highly unlikely event that the core of bone would remain fixed atits base, then with the drive mechanism 308 removed, a corkscrew 408shown in FIG. 14C is introduced though the central opening of rearportion 306 and threaded down and through the core of bone within 304and to the depth of teeth 302. The tip 318 of the corkscrew 408, whichextends substantially on line with the outer envelope of the corkscrew,then cuts radially through the base of the bone core. As the handleportion 314 of the corkscrew 408 abuts the flat, rearward surface ofportion 306 and it can no longer advance. As corkscrew 408 is continuedto be turned further, it will cause the core of bone to be pulledrearward, as in removing a cork from a wine bottle. Trephine 300 has abarrel portion 304 continuous with sharp toothed portion 302 having aninner diameter just less than the inner diameter of the spinal implant Ito be loaded.

Referring to FIG. 14B, the Trephine 300 with its core of harvested boneis then placed as shown in FIG. 14B, through opening 340 of Implant BoneLoading device 320, where the barrel portion 304 then passes through andis stopped by circular flange 344. The plunger shaft 326 of instrument320 is then prepared for attachment by rotating knob 332counterclockwise such that the plunger 372 is pulled via the longthreaded shaft portion 328 back to the base of collar 330 at itsproximal end. In this position, knob 332 is considerably extendedrearward from collar 330. With plunger shaft 326 in this position, theplunger head 372 is inserted into the central hollow of portion 306 ofTrephine 300 as the proximal cylindrical portion of collar 330 thenfollows it, such that the plunger 372 then occupies the rearward portionof barrel 304 and the proximal cylindrical portion of collar 330occupies the central hollow of portion 306. A pair of diametricallyopposed radially projecting arms 346 on collar 330 are then advancedlongitudinally into diametrically opposed paired L slots 340 and thenrotated clockwise to complete this assembly.

At the other end of instrument 320, a spinal implant I is engagedthrough its female rectangular slot 364 by a rectangular protruding barextending from rearward facing surface of end plug 324, (not shown) andsecured there by knob 334 which extends as a rod through a centralaperture within end plug 324 to extend at the id far end as a small boltwhich threads to a female aperture centered within the female slot 364of the spinal implant. With the spinal implant I secured to end plug 324and the opposite end of the implant I presenting as a hollow, tubularopening, end plug 324 is advanced into device 320 where it is secured byrotationally engaging diametrically opposed L-shaped slots 321. Withdevice 320 fully assembled, end 302 of trephine 300 lies coaxial andopposed to the open end of implant I.

Referring to FIG. 15, as knob 332 is then rotated clockwise, the plunger372 proximal the threaded shaft 328 is then forcibly, but controllablydriven forward down the barrel 304 ejecting the bone graft directly intothe spinal implant I. As the bone graft is greater in length than theinterior of the spinal implant, with further compression the bone isforced into the radially disposed apertures through the wall of thedevice communicating from the central cavity to the exterior.

End plug 324 is then removed from apparatus 320. Using end plug 324 as ahandle, end cap 374 shown in FIG. 16 is secured to the open end of thespinal implant I. The implant is then disassociated from end plug 324 byrotating, knob 334 counterclockwise.

Referring to FIG. 16, an Implant Driver instrument which may be used toeither insert or to remove said implant I is shown. Driver 350 has atits far end 362, a rectangular protrusion 398, which protrusionintimately engages the complimentary rectangular slot 364 of implant I.Protruding from slot 398 of end 362 is threaded portion 353, whichextends as a rod through hollow shaft 358 and hollow hand barrel 360 toknob 354 where it can be rotationally controlled. Threaded portion 353screws into a female aperture central slot 364, urging 353 into 364, andbinding them together such that instrument 350 can be rotated via pairedand diametrically opposed extending arms 366 and in either directionwhile maintaining contact with the implant.

Referring to FIG. 17, affixed to the Driver 350, the implant I is thenintroduced through the Outer Sleeve 140 and screwed into the interspaceopposed between the two prepared vertebrae V until such time as theleading edge of the Implant Cap 374 reaches the depth of the preparedhole at which time its forward motion is impeded by the bone lyingbefore it which had not been drilled out. This allows for a progressivefeel to the surgeon as the implant is screwed home.

As described previously, with the use of the Tap 280, this terminalresistance to further seating provides significant tactile feedback tothe surgeon. Again, as with the Tap 280, visual monitoring of the depthof insertion of the implant is provided to the surgeon by observing theprogressive approximation of the forward surface 370, of barrel portion360, as it approaches the rearward facing surface 172 of Outer Sleeve140. Nevertheless, a final safety mechanism, when the full depth ofinsertion has been achieved, surface 370 of instrument 350 will abutsurface 172 of the Outer Sleeve 140, prohibiting any furtherinstallation of the spinal implant.

Referring to FIG. 18, once the implant has been fully installed, theDriver 350 is dissociated from the implant I by turning knob 354 in acounterclockwise direction. The Driver 350 is then withdrawn from theOuter Sleeve 140, then the Outer Sleeve 140 is removed. This leaves theimplant fully installed and inset to the determined depth as shown inFIG. 18.

Attention is then redirected to the other, or first, side of the spine.A dural nerve root retractor is used to retract the neural structuresmedially, bringing into full view the head 128 of the Short Distractor120, lying flush on the canal floor. Utilizing apparatus 152, extendedscrew portion 116 is inserted into the female threaded portion 114 ofthe Short Distractor 120 as the extended rectangular portion 134 ofapparatus 152 is engaged to the female rectangular portion 118 of theShort Distractor 120. Then turning rearward facing portions 108 and 110,utilizing the knob 136 of FIG. 2, the Long Distractor configuration isrestored.

With the dural sac and nerve roots still retracted and protected, theOuter Sleeve 140 is slipped over the reconstituted Long Distractor andseated using the Driver Cap 162. The entire sequence of events asdescribed for the implantation of the spinal implant I as alreadyplaced, is then repeated such that both spinal implants come to lie sideby side within the interspace. Though not necessary, circlage or otherinternal fixation of the levels to be fused may additionally beperformed, and then the wound is closed in the routine manner.

Brief Discussion with Reference to the Drawings of the Preferred Methodand Instrumentation for Anterior Interbody Fusion IncorporatingIntercorporeal Predistraction and Utilizing a Guarded Sleeve System isDisclosed

Because of the absence of the spinal cord and nerve roots, it isgenerally possible to visualize in one instance the entire width of thedisc space from side to side throughout the cervical, thoracic, orlumbar spine. In the preferred embodiment of the anterior interbodyfusion, implants are placed side by side from anterior to posteriorparallel to the interspace and extending into the adjacent vertebralbodies. Where the transverse width of the disc space is insufficient toallow for the use of two implants, each of which would be large enoughto protrude to the required depth into the adjacent vertebrae, then asingular and significantly larger implant may be placed centrally. Withthis in mind, and in light of the very detailed description of thetechnique and instrumentation already provided in regard to the methodof posterior lumbar interbody fusion, a brief discussion of anteriorspinal interbody fusion with dual implant installation will suffice, andthe method for installation of a large, singular midline graft willbecome obvious.

The interspace to be fused is exposed anteriorly. The soft tissues arewithdrawn and protected to either side, and if necessary, above andbelow as well. It is then possible to visualize the entire width of thevertebrae anteriorly adjacent that interspace. As discussed above, thesurgeon has already templated the appropriate patient radiographs todetermine the requisite distraction and optimal implant size. In thepreferred method, the surgeon then broadly excises the great bulk of thenuclear disc portion. (Alternatively, the disc can be left to be removedvia the drill later.) The surgeon then notes and marks a point midwayfrom side to side anteriorly. He then inserts Long Distractor 100centering it on a point midway between the point just noted and thelateral extent of the intervertebral space visualized anteriorly. Theouter barrel portion 106 of the Distractor 100 utilized, will correspondto the outside diameter of the implants to be installed. The Distractortips 102 inserted are sequentially larger in diameter until the optimaldistraction is achieved. This optimal distraction, although suggested bythe initial templating, may be visually and tactilely confirmed asperformed. When the optimal distraction is achieved, the vertebralendplates will come into full congruence and parallel to the forwardshaft portion 102 of the Distractor 100, causing an alteration in thealignment of the vertebrae and a significant increase in theinterference fit and pressurization at the tip, such that the instrumentbecomes exceedingly stable.

There is a sensation imparted to the surgeon of the tissues having movedthrough their elastic range to the point where the two adjacentvertebrae V begin to feel and move as if a single solid. These changesare easily appreciated visually as the vertebrae realign to becomecongruent to, tip 102, and can also easily be appreciated via lateralRoentgenography. However, should the surgeon fail to appreciate thatoptimal distraction has been achieved and attempt to further distractthe interspace, he would find that extremely difficult to do because ofthe increased resistance as the tissues are moved beyond their range ofelastic deformation. Further, there would be no elasticity left to allowthe vertebrae to move further apart and the sensation to the surgeonshould he attempt to gently tap the oversized Distractor forward with amallet, would be one of great brittleness.

Returning now to the procedure, when the correct intercorporeal LongDistractor 100 producing the ideal interspace distraction-having itsbarrel portion 106 corresponding to the implant I to be installed hasbeen inserted, then its exact duplicate is inserted anteriorlyequidistant to the other side of the spine. As the barrel portion 106 ofLong Distractor 100 is exactly of the same major diameter as the spinalimplant I looking coaxially on end, the surgeon can then asses theanticipated side by side relationship of the dual implants whenimplanted.

Referring to FIGS. 7C and 7D, a Dual Outer Sleeve 340 consisting of apair of hollow tubes is then introduced over the side by side LongDistractors 100 protruding anteriorly from the spine. The Dual OuterSleeve 340 is comprised of two hollow tubular members identical in sizedisplaced from each other ideally the sum of the difference between theminor and major diameters of both implants combined, but not less thanthat difference for one implant, as it is possible to have the threadsof one implant nest interposed to the threads of the other, such thatthey both occupy a common area between them. However, while thepreferred embodiment is slightly greater than two times the differencebetween the major and minor diameters of the implant (the sum of both)the distance may be considerably greater. Whereas in the preferredembodiment the paired tubular portions 348 of the Dual Outer Sleeve 340are parallel, when the area between them 350, is sufficiently great,these elements may be inclined or declined relative to each other suchthat they either converge or diverge at their proximal ends. The pairedtubular portions 348, may be bridged in part or wholly throughout theirlength, but are rigidly fixed by Foot Plate 344. In its preferredembodiment, a top view shows the Foot Plate 344 to be essentiallyrectangular, but without sharp corners. However, it is appreciated thatother shapes for the Foot Plate 344 can be utilized.

Referring to FIG. 7D, it can be appreciated, that Foot Plate 344 iscontoured so as to approximate the shape of the vertebrae anteriorly.Extending forward from Foot Plate 344 are multiple sharp prongs 342sufficiently long to affix them to the vertebrae. The prongs 342 arelimited in length so as to not penetrate too far posteriorly and numberfrom 2 to 10, but preferably 6.

Referring to FIGS. 7E and 7F, as the Dual Outer Sleeve 340 is drivenforward utilizing Dual Driver Cap 420, of FIG. 7E, engaging the rearwardend 352, the prongs 342 extending from Foot Plate 344 are embedded intothe opposed vertebral bodies until their forward motion is inhibited bythe curved Foot Plate 344 becoming congruent to and being stopped by,the anterior aspect of the vertebral bodies.

As already shown in FIG. 5, the Dual Driver Cap 420 is of the samedesign as Single Driver Cap 160, in that there is a recess 354 as per168, allowing the Outer Sleeve to be fully seated without impeding therearward projection of the Long Distractor unit. However, unlike in Cap160, area 354 is more relieved as it is unnecessary for the Dual Cap 420to contact the Long Distractor through portion 110 to inhibit itsforward motion, as the Foot Plate 344 functions to that effect. Further,the Dual Cap 420 for the Dual Outer Sleeve 340 is correspondingly dualitself and engages the rearward facing dual tubular portion 352. Oncethe Dual Outer Sleeve has been fully seated, the vertebrae adjacent theinterspace to be fused are rigidly held via Foot Plate 344 and theprongs 342. Thus, it is possible to remove either one, or if desired,both of the Long Distractor rods utilizing Long Distractor puller 200,as per the method already described. It is then the surgeon's choice towork on one or both sides of the spine. As per previous discussion, thesurgeon may drill the interspace utilizing the Inner Sleeve 242 or leavethe Long Distractors in place as per the “Trephine Method”.

Tapping, if necessary, and the insertion of the implants then occursthrough the protective Outer Sleeve 340. Once the implants have beenfully inserted, the Outer Sleeve is removed.

Having utilized the Drill method, or “Trephine Method”, with or withoutan Inner Sleeve to prepare the fusion site, it is the preferredembodiment to leave the Outer Sleeve 340 in place as it provides for theideal placement and alignment of the Tap 280 and implant I.

It is anticipated that the surgeon wishing to work deep within theinterspace, or preferring the ability to directly visualize the tapbeing used, or the implant being inserted, may choose to remove theOuter Sleeve after the insertion of the first prosthesis to maintainstability, or prior to that, which while not the preferred embodiments,are nevertheless within the scope of the present invention.

Alternative Methods to the Preferred Embodiment for Method of AnteriorInterbody Fusion

As previously described for the posterior lumbar spine, alternatively,one can employ the “Trephine Method” as has been described in detail.

As a further alternative, it should be noted that the key element in theanterior method is the use of the predistraction principle, where suchdistraction is maintained by the Outer Sleeve with or without the LongDistractor. Therefore, once the preparation of the interspace has beencompleted, while not the preferred embodiment, it is nevertheless withinthe scope of this invention that one could remove the Outer Sleeve asthere are no neural structures requiring protection, and insert theimplants directly rather than through the Outer Sleeve.

As yet a further alternative of this method, where the height of thedistracted interspace is such that the diameter of the implant requiredto span that height and to embed with sufficient depth into the opposedvertebral bodies is such that it is not possible to place two suchimplants side by side, then only a single implant which may be ofsignificantly increased diameter, is used and placed centrally withinthe interspace rather than to either side. The placement of a singularcentral graft via the present invention method and instrumentation is inkeeping with the methods already described and can be performed usingeither a drill or the “Trephine Method”.

Referring to FIGS. 16-18, a cylindrical embodiment of the spinal implantI of the present invention is shown. In FIG. 16 the implant I is shownattached to the insertion device 350. In FIGS. 17 and 18 the implant Iis shown installed in the disc space D, between the adjacent vertebrae.

The cylindrical implant I comprises a hollow tubular member which in thepreferred embodiment is made of an ASTM surgically implantable material,preferably titanium. The cylindrical implant I is closed at one end andopen at the other end covered by a cap 394. The cylindrical implant Ihas a series of macro-sized openings 390 through the side walls of thecylindrical implant I. A series of external threads 392 are formed onthe circumference of the cylindrical implant I. Any variety of threadsmay be used on the implant. The cap 374 has a hexagonal opening 394 fortightening the cap 374.

While the present invention has been described with respect to thepreferred embodiment of the method and instrumentation, it isappreciated that other embodiments of the method and instrumentation maybe devised without departing from the scope of the present invention.Examples of further embodiments of the present invention are describedin detail below.

Detailed Description of Alternative Embodiments of Apparatus and Method

When the human spine is viewed from the side, it consists of a balancedseries of curves, as opposed to the vertebrae being stacked one uponanother in a straight line when viewed from the side. In both thecervical and lumbar regions of the spine, the vertebrae relate to eachother so as to form curves where the apex of said curves is displacedforward within the body, and those segments of the spine are said to bein lordosis. In contradistinction, in the thoracic portion of the spine,the vertebrae relate to each other so as to form a curve where the apexof said curve is displaced posteriorly and is said to be in kyphosis.The methods and instrumentation of the present invention have as one ofits purposes to provide for the permanent stabilization of contiguousvertebrae by fusion, there is then a need for a means to preserve saidlordosis/kyphosis if present, or to restore said lordosis/kyphosis ifalready lost, prior to the completion of the fusion procedure.

The following embodiments of the present invention, either individuallyor in combination, provide for both the stabilization and fusion to beperformed with the related vertebrae in the correct anatomic lordosis orkyphosis. Where it is possible to approach the spine from various angleseach of the devices, then has different forms appropriate to thatspecific approach.

Referring to FIG. 19, an alternative embodiment of the instrumentationof the present invention comprising a Posterior Long Lordotic Distractor400 capable of restoring and maintaining lordosis of adjacent vertebraeV from the posterior approach of the spine is shown. The Posterior LongLordotic Distractor 400 is inserted from the posterior aspect of thespine and comprises a barrel portion 410 terminating at its distal end412 in a disc penetrating portion 420 which is shown interposed withinthe disc space between two adjacent vertebrae V. The disc penetratingportion 420 terminates distally into a leading bullet-shaped front end422 which facilitates the insertion of the disc penetrating portion 420between the adjacent vertebrae V. The disc penetrating portion 420 isconfigured to have an uneven diameter such that it has a lesserdiameter, and thus a lesser height within the disc space proximate thedistal end 412 of the barrel portion 410 and has a greater diameter, andthus greater height within the disc space, in the direction of the frontend 422. This configuration of the disc penetrating portion 420 servesto not only restore the intervertebral disc space height upon insertionof the disc penetrating portion 420 of the Posterior Long LordoticDistractor 400, but also serves to restore and maintain the normallordosis between the adjacent vertebrae V. The leading bullet-shapedfront end 422 is of particular importance in regard to the PosteriorLong Lordotic Distractor 400 where the largest diameter portion of thedisc penetrating portion 420 would otherwise be entering the disc spacefirst.

The widest diameter of the disc penetrating portion 420 is less than thediameter of the barrel portion 410, such that a circumferential shoulder424 is formed at the distal end 412 of the barrel portion 410 whichprevents over penetration into the disc space of the Posterior LongLordotic Distractor 400. It can readily be appreciated that such aconfiguration of the disc penetrating portion 420 renders the PosteriorLong Distractor 400 quite stable within the disc space and resistant tobacking out as the compressive forces of the spine upon the discpenetrating portion 420 tend to urge it forward, while simultaneouslythe circumferential shoulder 424 makes such further motion impossible,thus making the Posterior Long Distractor 400 exceedingly stable.

Referring to FIG. 20, in preparation for the bone removal step, thePosterior Long Lordotic Distractor 400 is shown with the discpenetrating portion 420 in place between the adjacent vertebrae V torestore and maintain lordosis of the spine. An Outer Sleeve 140described above in reference to FIG. 5, is properly seated over thePosterior Long Lordotic Distractor 400 using a mallet and the alreadydescribed Driver Cap 160. While the bone removal step may be performedby either the drilling method described above in reference to FIGS. 11Aand 11C or the “Trephine Method” described above in reference to FIG.11B, the “Trephine Method” is preferred in this situation as it leavesthe Posterior Long Lordotic Distractor 400 undisturbed until sufficientspace has been created by the removal of bone at least as great as thethickness of the wall of the trephine 270 itself to allow for theunobstructed removal of the Posterior Long Lordotic Distractor 400.

If the “Trephine Method” described above in reference to FIG. 11B isused with the Posterior Long Lordotic Distractor 400 the Outer Sleeve140 would first be fitted with an Inner Sleeve 242 such as that shown inFIG. 11B, prior to both being placed simultaneously down over the barrelportion 410 of the Posterior Long Lordotic Distractor 400. Once theOuter Sleeve 140 is concentrically seated relative to the barrel portion410, the Inner Sleeve 242 alone would be removed, and the trephine 270would then be placed over the Posterior Long Lordotic Distractor 400 andwithin the confines of the Outer Sleeve 140 and into the adjacentvertebrae V across the disc space to the appropriate depth. The use ofan Inner Sleeve is not required as the trephine 270 is both centered andaligned by the Posterior Long Lordotic Distractor 400.

In addition to cutting the two hemi-cylinders of bone, one for eachvertebrae V, the saw-like sharp cutting teeth 271 of the trephine 270shown in FIG. 11B removes a path of bone equal to the distance of thesplaying out of each of the cutting teeth 271 relative to its neighborand which distance cannot be less than the wall thickness of thetrephine 270 itself. Thus, once the trephine 270 is removed, left behindis a semi-cylindrical space outlining each of the arcs of bone cut fromthe adjacent vertebrae V such that the two spaces combined provide forsufficient space such that it is then possible to extract the PosteriorLong Lordotic Distractor 400 without disturbing the vertebrae Vthemselves as the vertebrae V are held in position by the Outer Sleeve140 which engages both of the vertebrae V.

Referring to FIGS. 21 and 22, since the vertebrae V are placed intolordosis prior to the bone removal step, the space S created by the boneremoval is cut at an angle relative to the vertebrae V in the shape of acylinder, and which corresponds to the shape of the cylindrical implantI. In this manner, the cylindrical implant I with parallel walls may beinserted between adjacent vertebrae V which have been stabilized forfusion in angular relationship to each other so as to preserve thenormal curvature of the spine.

Referring to FIGS. 23 and 24, an elevational side view and a top planview, respectively, of a Posterior Short Lordotic Distractor 500 forposterior use generally referred to by the numeral 500 is shown. ThePosterior Short Lordotic Distractor 500 is similar to the ShortDistractor 120 described above in reference to the ConvertibleDistractor and comprises a disc penetrating portion 520 identical tothat of the Posterior Long Lordotic Distractor 400 and an increaseddiameter head 128 as described above in reference to FIGS. 3-3F. Asdiscussed above for the Posterior Long Distractor 400, the configurationof the disc penetrating portion 520 renders the Posterior Short LordoticDistractor 500 quite stable. This is an especially important feature forthe Posterior Short Lordotic Distractor 500 because it is left under thedelicate dural sac and nerves while work is being performed on thecontralateral side of the spine. If the Posterior Short LordoticDistractor 500 were other than stable, injury to these structures mightresult. To further prevent unwanted backing out of the Posterior ShortLordotic Distractor 500, the bone engaging surface 530 may be knurled orotherwise roughened, or have forward facing ratchetings.

Referring to FIG. 25, an Anterior Long Lordotic Distractor 600 for useanteriorly within the spine is shown. It can be seen that theconfiguration of the disc penetrating portion 620 is the reverse of thedisc penetrating portion 420 of the Posterior Long Lordotic Distractor400 in that the disc penetrating portion 620 is of greatest diameter andheight proximate the barrel portion 610 and that the diameter and heightare diminished more distally in the direction towards the front end 622along the disc penetrating portion 620. The Anterior Long LordoticDistractor 600 serves to restore and maintain lordosis of the spine bydistraction of the adjacent vertebrae V. As described above for thePosterior Short Lordotic distractor 500, it is appreciated that anAnterior Short Lordotic Distractor (not shown) having a disc penetratingportion 520 may be similarly devised.

It can be seen that all of the lordotic distractors, both the anteriorand the posterior embodiments, have specialized leading bullet-shaped ornosecone-shaped portions so as to facilitate the insertion of the discpenetrating portions within the disc space. This is of particularimportance in regard to the Posterior Lordotic Distractors where thelargest diameter portion of the disc penetrating portion 420 wouldotherwise be entering the disc space first.

Referring to FIGS. 26 and 27, an alternative embodiment of the presentinvention for maintaining distraction during the surgical procedureinvolves a more specialized form of the previously described OuterSleeve 140 and is shown and identified as the Extended Outer Sleeve 700.The Extended Outer Sleeve 700 comprises a hollow tubular member 702having a distal end 710 which has been extended such that a pair ofextended portions 720 and 722, which are essentially a continuation ofthe hollow tubular member 702 itself (with or without reinforcement),are opposed 180 degrees from each other, tapered at their leading edges724 and 726 for ease of introduction, and of such height as to restorethe height of the intervertebral disc space. Located at the distal end710 may be a plurality of teeth 712, similar to those previouslydescribed above, or other engagement means for engaging the bone of theadjacent vertebrae V. It appreciated that the distal end 710 may have noteeth 712.

The Extended Outer Sleeve 700 is entirely a new invention such as hasnever existed in the art or science of surgery, the Extended OuterSleeve 700 offers numerous advantages over all previously describeddrilling sleeves and the Outer Sleeve 140 herein previously described.The Extended Outer Sleeve 700 by dint of its extended portions 720 and722 which are inserted between the adjacent vertebrae does itself act asan intervertebral distractor and is therefore essentially a combinationouter sleeve and distractor. The Extended Outer Sleeve 700 isexceedingly stable as the extended portions 720 and 722 are trappedwithin the disc space and further held there by the considerablecompressive loads within the spine.

Referring to FIG. 28, because of the stability thus provided, a furtherderivative advantage is that the teeth 772 on the distal end 710 of theExtended Outer Sleeve 700′ may either be eliminated as shown in FIG. 28,or in the preferred embodiment be made of a lesser size. Further, itshould be noted that teeth 712 when present would be confined to thearea directly in line with the vertebrae V and the extended portions 720and 722 would ensure the proper rotatory alignment.

A further advantage, to be discussed in more detail subsequently, isthat the extended portions 720 and 722 confine the surgery to the areawithin and between the extended portions 720 and 722 and protect allother tissues external to the extended portions 720 and 722.

Having now described the novel concept of the Extended Outer Sleeve 700,attention may now be directed to further variations of the ExtendedOuter Sleeve 700 capable of not only restoring and maintaining theappropriate intervertebral disc space height, but additionally beingable to restore and maintain anatomic lordosis or kyphosis, as desired,throughout the surgical procedure.

Referring to FIG. 29, a Posterior Lordotic Extended Outer Sleeve 800 foruse from the posterior approach of the spine is shown. The PosteriorLordotic Extended Outer Sleeve 800 comprises a hollow tubular member 802having a distal end 810 which has been extended such that a pair ofextended portions 820 and 822, which are essentially a continuation ofthe tubular member 802, are opposed 180 degrees from each other. Theextended portions 820 and 822 differ from the extended portions 720 and722 in that the extended portions 820 and 822 are configured to restoreand maintain lordosis of the spine similar to the disc penetratingportion 420 of the Posterior Long Lordotic Distractor 400, the featuresof which are herein incorporated by reference.

The extended portions 820 and 822 each have a height that is lesser at apoint proximate the distal end 810 of the tubular member 802 thatincreases in the direction away from the tubular member 802. Theextended portions 820 and 822 are tapered at their leading edges 824 and826, respectively to facilitate insertion into the disc space.

Between the extended portions 820 and 822, may be a plurality of teeth812 for engaging the bone of the vertebrae V when the Extended OuterSleeve 800 is inserted within the disc space between the adjacentvertebrae V.

Referring to FIG. 30, a Posterior Lordotic Extended Outer Sleeve 800′ inplace within the intervertebral disc space is shown.

Referring to FIG. 31, an Anterior Extended Outer Sleeve 900′ for usefrom the anterior approach of the spine is shown. The Anterior LordoticExtended Outer Sleeve 900 comprises a hollow tubular member 902 having adistal end 910 which has been extended such that a pair of extendedportions 920 and 922 which are essentially a continuation of the tubularmember 902 and are opposed 180 degrees from each other. The extendedportions 920 and 922 differ from the extended portions 820 and 822 inthat the extended portions 920 and 922 are configured to restore andmaintain lordosis of the spine from the anterior approach similar to thedisc penetrating portion 620 of the Anterior Long Lordotic Distractor600, the features of which are herein incorporated by reference.

The extended portions 920 and 922 each have a height that is greater ata point proximate to the distal end 910 of the tubular member 902 thatdecreases in the direction away from the tubular member 902. Theextended portions 920 and 922 are tapered at their leading edges 924 and926, respectively to facilitate insertion into the disc space.

While the Lordotic Extended Outer Sleeve for use anteriorly is shown inthe singular form and in use in the lumbar spine, it is understood thatit may take a double barrelled form and in either form, be usedthroughout the spine.

Referring to FIGS. 33 and 34, a Lumbar Dual Extended Outer Sleeve isshown and generally referred to by the numeral 1100. The Dual ExtendedOuter Sleeve 1100 comprises two hollow tubular members 1101 and 1102.The two hollow tubular members 1101 and 1102 have a distal end 1104which has been extended to form an extended portion 1121 which isessentially a continuation of the hollow tubular members 1101 and 1102joined together. The extended portion 1121 is similar in shape andfunction to the extended portions 920 and 922 described above inreference to FIG. 31. The extended portion 1121 has a height that isgreater at a point proximate the distal end 1104 and decreases in thedirection away from the hollow tubular members 1101 and 1102, in orderto maintain the normal curvature of the spine by correcting the angularrelationships of the vertebrae V. The extended portion 1121, is taperedat its leading edge 1124 to facilitate insertion of the extended portion1121 into the disc space between two adjacent vertebrae V. Located atthe distal end of the tubular members 1101 and 1102 are sharpened teeth1130 for engaging the vertebrae V.

Each of the hollow tubular members 1101 and 1102 are displaced from eachother ideally the sum of the difference between the minor and majordiameters of two threaded spinal implants I combined, but not less thanthat difference for one implant I, as it is possible to have the threadsof one implant I nest interposed to the threads of the other implant Isuch that they both occupy a common area between them. Typically, thewalls of each hollow tubular members 1101 and 1102 have a combinedthickness at the point which the walls of the hollow tubular members1101 and 1102 are in contact with each other which is approximately 2.0mm. This is achieved by machining away part of each hollow tubularmember 1101 and 1102 to reduce the wall thickness of each hollow tubularmember 1101 and 1102 prior to joining them together. In this manner, thetwo hollow tubular members 1101 and 1102 may be placed closer togetherso that two spinal implants I may be placed closer together wheninserted within the disc space between adjacent vertebrae W. The hollowtubular member 1101 and 1102 can be overlapped or displaced from eachother so as to control the distance between implants when the DualExtended Outer Sleeve is utilized and two implants implanted

The hollow tubular members 1101 and 1102 may be bridged in part orwholly throughout their length, but are typically fixed by a foot plate1110, similar in function, but not in configuration, to Foot Plate 344described above in reference to FIGS. 7C and 7D.

Referring specifically to FIG. 34, the foot plate 1110 has an ovalconfiguration that contours and hugs the vertebrae and has a pluralityof prongs 1112-1115 extending from the bottom of the foot plate 1110 isshown. The prongs 1112-1115 are sufficiently long to engage the bone ofadjacent vertebrae V, but limited in length so as not to over penetratebeyond the vertebrae once inserted.

Referring to FIG. 35, a second Dual Extended Outer Sleeve 1200, isshown. The Dual Extended Outer Sleeve 1200 is similar to the DualExtended Outer Sleeve 1100, except that it has additional extendedportions 1220 and 1222 which have a height that is greater near thedistal end 1204 of the hollow tubular members 1201 and 1202 anddecreases in the direction away from the hollow tubular members 1201 and1202. The extended portions 1220-1222 are similar in shape and functionto the extended portions 920 and 922 described above in reference toFIG. 31. Moreover, as the foot plate 1210 is rectangular, and largerthan foot plate 1110, additional prong 1216 and 1217 may be added.

Further, it should be appreciated that the lordotic distractor for useposteriorly when referring to their use in the lumbar spine, would beused anteriorly if applied to the thoracic spine, either in the singleor double-barrel form. This is because the thoracic spine is normallycurved into kyphosis which is the reverse of lordosis. That is, inapproaching the thoracic spine anteriorly, it would be desirable todistract the back of the disc space more than the front, and that wouldrequire an Extended Outer Sleeve which would resemble that seen in FIG.30; though when used in this new context, it would more correctly bereferred to as an Anterior Thoracic Kyphotic Extended Outer Sleeve. Aswith the Posterior Lordotic Outer Sleeve, the Posterior and AnteriorLong Lordotic Posterior Short Lordotic Distractor and Anterior ShortLordotic Distractors, though referred to previously as lordotic whenplaced into the lumbar spine from the posterior approach, would now morecorrectly, when placed in the thoracic spine from the anterior approachbe called Kyphotic Thoracic Distractors.

It can readily be appreciated that the described Extended Outer Sleevesmay be used with the Short and Long Distractors having a discpenetrating portion of uniform diameter or in combination with thelordotic and kyphotic distractors of complimentary configuration.

Referring to FIGS. 36-41, shown is the apparatus 1350 for use ininstalling an improved interbody spinal fusion implant 1300 having oneor more flat sides as disclosed in co-pending application filed on Feb.17, 1995, entitled IMPROVED INTERBODY SPINAL FUSION IMPLANTS which isincorporated herein by reference. The apparatus 1350 comprises a DualOuter Sleeve 1310 having a pair of overlapping, hollow cylindrical tubes1352 and 1354 identical in size and each having an internal diameterslightly larger than the outer diameter of the spinal fusion implant1300. The cylindrical tubes 1352, 1354 are in communication with eachother along their length and are displaced from each other ideally adistance that is slightly greater than the sum of the diameters of twospinal fusion implants 1300 placed side-by-side with the flat sides 1302of each spinal fusion implant 1300 touching. The cylindrical tubes 1352and 1354 are joined longitudinally such that they are partiallyoverlapping. The hollow cylindrical tubes 1352 and 1354 are mounted on afoot plate 1362 similar to the foot plate described in FIG. 35. Thereare a series of prongs 1364 a-1364 f projecting from the bottom 1366 ofthe foot plate 1360 which are used to engage the Dual Outer Sleeve 1310to the base of the adjacent vertebrae V.

Referring specifically to FIG. 36, the apparatus 1350 is introduced overtwo Long Distractors 1320 and 1322 placed side-by-side and protrudinganteriorly from the vertebrae V. The Long Distractors 1320 and 1322 aresimilar to the Long Distractor 100 described above except that they havea flat side 1324 and 1326, respectively.

Referring to FIGS. 37 and 38, in one embodiment, the foot plate 1360 isessentially rectangular, but without sharp corners. It is appreciated bythose skilled in the art, that other shapes can be utilized.

As shown in FIGS. 36 and 39, the foot plate 1360 is contoured so as toapproximate the external curvature of the vertebrae V anteriorly.Extending forward from foot plate 1360 are the multiple sharp prongs1364 a-1364 f which are sufficiently long to permit fixation of the footplate 1360 to the vertebrae V. The prongs 1364 a-1364 f are limited inlength so as to not penetrate the vertebrae V too far posteriorly andnumber from 2 to 10, but preferably 6.

Referring to FIG. 39, as the Dual Outer Sleeve 1350 is driven forward,the prongs 1364 a-1364 f extending from foot plate 1360 are embeddedinto the opposed vertebrae V until their forward motion is inhibited bythe foot plate 1360 becoming congruent to and being stopped by, theanterior aspect of the vertebrae V.

As shown in FIG. 36, once the apparatus 1350 has been fully seated, thevertebrae V adjacent the interspace D to be fused are rigidly held viafoot plate 1360 and the prongs 1364 a-1364 f. Thus, it is possible toremove either one, or if desired, both of the long distractors 1320 and1322. The dual outer sleeve has been described above for inserting twoimplants each having at least one flat side, may have extended portionsfor intradiscal insertion which are capable of producing distraction aswell as kyphosis or lordosis as previously described with suchextensions extending in line with the lateral walls of the cylindricaltubes.

Referring to FIG. 40, once the Dual Outer Sleeve 1350 has been fullyseated, one of the Long Distractors 1320 and 1322 is removed and thesurgeon may drill the interspace D utilizing drill 250 using each of thehollow cylinders 1352, 1354 to guide the drill 250 in order to createoverlapping holes in which the spinal fusion implants 1300 a and 1300 bmay be inserted. It is also appreciated by those skilled in the art,that a hollow inner sleeve (not shown) may be inserted into the hollowcylinders 1352, 1354 through which the drilling is performed or the LongDistractors may be left in place and a hollow trephine that fits overeach of the Long Distractors 1320 and 1322 may be used to drill theinterspace D. It is readily appreciated that the tubular members can beof a variety of shapes and sizes. Further, the removal of disc and bonemay be accomplished by the use of a burr, or a chisel of appropriateshape for that purpose and with or without the use of a drill. Theimplants would then have shapes appropriate for use in the spaces soformed.

Referring to FIG. 41, once the interspace D has been drilled, an implantDriver 350 described above is used to insert the spinal fusion implants1300 a and 1300 b preferably by linear advancement. The implant driverinstrument 350 may be used to either insert or to remove the spinalfusion implants 1300 a and 1300 b.

Once affixed to the implant Driver 350, the spinal fusion implant 1300 ais then introduced through one of the hollow cylindrical tubes 1352,1354and driven into the interspace D by the application of an impactionforce transmitted through the implant driver instrument 350. Once thespinal fusion implant 1300 a is inserted into the interspace D, thesurface roughenings of the outer surface of the spinal fusion implant1300 a engage the bone of the vertebrae V and the implant Driver 350 isdetached from the spinal fusion implant 1300 a. The implant driverinstrument 350 is then withdrawn from the Dual Outer Sleeve 1350 and thespinal fusion implant 1300 a is fully installed and inset in theinterspace D as shown in FIG. 41.

Once a first spinal fusion implant 1300 a is inserted into theinterspace D, a second spinal fusion implant 1300 b is driven into theinterspace D so that the flat side 1302 a or 1302 b of each spinalfusion implant 1300 a and 1300 b are adjacent to each other and aretouching. In this manner, two spinal fusion implants 1300 a and 1300 bare implanted within the interspace D and engage the bone of theadjacent vertebrae V without exceeding the width of the spinal column.It is appreciated that there are other ways that two spinal implants canhave complimentary shapes and that they can be inserted by linearadvancement through a single (both at once) or dual outer sleeve havingintradiscal extended members for stabilization, distraction, and/or toeffect lordosis or kyphosis.

While the present invention has been described in association with theimplant of a threaded spinal implant, it is recognized that other formsof implants may be used with the present method. For example, dowels,made from bone or artificial materials, knurled or irregularly shapedcylinders or partial cylinders, or any other shaped implants that can beintroduced through the outer sleeve may be used. Being able to performthe procedure through the outer sleeve permits the procedure to beperformed safely and quickly, and more accurately.

What is claimed is:
 1. A method for performing a surgical procedure, comprising the steps of: providing a surgical retractor including an elongate member defining a longitudinal axis, the elongate member including proximal and distal end portions and defining an opening therethrough to receive instrumentation, the distal end portion configured for insertion at least partially into an intervertebral space between adjacent opposed vertebrae and having two spaced apart retractor arms, each retractor arm including first and second supporting surfaces laterally displaced with respect to each other and to the longitudinal axis; distracting the adjacent vertebrae by at least partially inserting the retractor arms of the retractor within the intervertebral space whereby the first supporting surface of each retractor arm engages one vertebrae and the second supporting surface of each retractor arm engages the other vertebrae such that the adjacent opposed vertebrae are laterally displaced; and performing the surgical procedure.
 2. The method according to claim 1 wherein the step of performing includes introducing surgical instrumentation within the opening of the surgical retractor, the surgical instrumentation being utilized to perform the surgical procedure.
 3. The method according to claim 2 wherein the step of performing the surgical procedure includes introducing a fusion implant through the opening in the surgical retractor and between the distracted vertebrae to effect fusion thereof.
 4. A method for fusing adjacent vertebral bodies, comprising the steps of: a) accessing the intervertebral disc space; b) providing a retractor including a retractor sleeve having proximal and distal end portions, the distal end portion having opposed retractor arms extending in a general longitudinal direction; c) positioning the retractor arms within the intervertebral disc space whereby first and second supporting surfaces of each arm contact opposed vertebral bodies; d) introducing a drill instrument into the sleeve and advancing the drill instrument within the sleeve to the disc space; e) forming with the drill instrument a bore that penetrates at least partially into each opposed vertebral body; f) removing the drill instrument from the sleeve; and g) introducing a fusion implant into the bore.
 5. The method according to claim 4 further including the steps of: h) introducing a tap instrument into the sleeve and advancing the tap instrument within the sleeve to the disc space; i) tapping with the tap instrument a thread within the bore; j) removing the tap from the retractor sleeve; k) introducing into the sleeve a fusion cage having a cage body with an external thread; and l) screwing the cage body into the threaded bore.
 6. The method according to claim 5 wherein the step of introducing a fusion implant includes introducing a fusion implant having a plurality of openings extending through the cage body.
 7. The method according to claim 6 further including the step of filling the cage body with bone-growth inducing substances.
 8. The method according to claim 7 further including the step of mounting an end cap to the open end of the cage body to enclose the bone-growth inducing substances within the cage body.
 9. The method according to claim 4 wherein the retractor arms define a dimension between the first and second supporting surfaces sufficient to distract the opposed vertebral bodies and wherein the step of positioning the retractor arms includes distracting the opposed vertebral bodies.
 10. A method for performing a surgical procedure comprising: providing a surgical retractor including an elongate sleeve member having proximal and distal end portions and defining an opening therethrough to receive instrumentation, the distal end portion configured for insertion at least partially into an intervertebral space between adjacent opposed vertebrae; distracting the adjacent vertebrae by at least partially inserting the distal end portion of the sleeve member within the intervertebral space; inserting instrumentation through the opening in the surgical retractor; and performing the surgical procedure.
 11. The method according to claim 10 wherein the step of performing the surgical spinal procedure includes utilizing the instrumentation inserted through the opening in the surgical retractor to perform the surgical spinal procedure.
 12. The method according to claim 11 wherein the elongate sleeve member of the surgical retractor defines an axial opening and wherein the step of inserting includes positioning instrumentation through the axial opening to perform the surgical spinal procedure.
 13. A method for performing a surgical procedure comprising: providing a surgical retractor including an elongate hollow member having proximal and distal end portions, the distal end portion having first and second stationary retractor arms configured for insertion at least partially into an intervertebral space defined between upper and lower opposed vertebrae; distracting the adjacent vertebrae to a predetermined distracted position by at least partially inserting the retractor arms within the intervertebral space; and performing the surgical procedure.
 14. The method according to claim 13 wherein each retractor arm includes first and second opposed supporting surfaces and wherein the step of distracting includes at least partially inserting the retractor arms whereby the first and second supporting surfaces of each retractor arm respectively engage the upper and lower vertebrae. 